Oracle DBA
Interview
Questions and Answers

Compiled
By
Mohamed Fowjil Abdul Hameed

Contents Oracle DBA Interviews - Overview 2 Oracle DBA Interview Questions and Answers – ARCHITECTURE 4 SENIOR ORACLE DBA INTERVIEW QUESTIONS 31 MID LEVEL ORACLE DBA INTERVIEW QUESTIONS 57 Oracle 11g Database New Features Interview Questions and Answers 65 Oracle RAC Interview Questions and Answers 70 Oracle RAC Interview Questions (10g) Questions and Answers 137 Oracle Data Guard Interview Questions and Answers 168 Oracle ASM Interview Questions and Answers 205 Oracle Patching,Cloning and Upgrade Interview Questions and Answers 219 Oracle Backup and Recovery Interview Questions and Answers 228 Oracle RMAN Interview Questions and Answers 232 Oracle Performance Tuning Interview Questions and Answers 237 Oracle Performance Tuning Interview Questions and Answers 245 Oracle Export/Import (exp/imp)- Data Pump (expdp/imp) Interview Questions and Answers 249 UNIX Interview Questions and Answers for Oracle DBAs 254

Oracle DBA Interviews - Overview
Dear Readers,
Hereby, I am sharing my experience of interviews asd technical discussion with various MNC Dba’s, Project managers and Project delivery managers and Technical architects, as part of my interview preparation, I used to refer my own work note as well as web sources below details are a consolidate form of my interview preparation and Oracle dba interviews questions and answers
General Guide line:
Interview Preparation
The most qualified job seekers need to prepare for job interviews. Interviewing is a learned skill, and there are no second chances to make a great first impression.
Google the Company!
Not being able to answer the question “What do you know about this company?” might just end your quest for employment, at least with this employer. Background information including company history, locations, divisions, and a mission statement are available in an “About Us” section on most company web sites. Review it ahead of time, then print it out and read it over just before your interview to refresh your memory.
Read the Job Description
It is imperative that you review the job description and the skills requested. Be able to articulate how your experience fits the need and how you can add value.
Introductions
It is important to communicate well with everyone you meet in your search for employment. It is, however, most important to positively connect with the person who might hire you. Shake hands, make eye contact, exude confidence, sit after the interviewer has sat down, engage the person you are speaking with, and you will let the interviewer know you are interested in the position. Insure you do this before you even answer any interview question.
Practice Good Nonverbal Communication
Insure you demonstrate confidence: standing straight, making eye contact and connecting with a good, firm handshake. That first impression can be a great beginning — or quick ending – to your interview.
Stay Calm
During the interview try to remain as calm as possible. Ask for clarification if you’re not sure what’s been asked and remember that it is perfectly acceptable to take a moment or two to frame your responses so you can be sure to fully answer the question.
Listen
From the very beginning of the interview, your interviewer is giving you information, either directly or indirectly. If you are not hearing it, you are missing a major opportunity. Good communication skills include listening and letting the person know you heard what was said. Observe your interviewer, and match that style and pace. Make sure you listen to the question and take a moment to gather your thoughts before you respond.
Communication Skills
Insure you speak slowly and clearly articulate your responses to questions. Do not allow your mouth to run ahead of your brain.
Answer the Questions
When an interviewer asks for an example of a time when you did something, he is seeking a sample of your past behavior. Do not be afraid to share projects that have gone awry, but be sure to follow it up with what you did to get the project back on track. If you fail to relate a specific example, you not only don’t answer the question, but you also miss an opportunity to prove your ability and talk about your skills.
Do Not Talk Too Much
There is nothing much worse than interviewing someone who goes on and on and on… The interviewer really doesn’t need to know your whole life story. Keep your answers succinct, to-the-point and focused and don’t ramble – simply answer the question.
Insure You Talk Enough
It’s really hard to communicate with someone who answers a question with a word or two. I remember a couple of interviews where I felt like I was pulling teeth to get any answers from the candidate. It wasn’t pleasant. So, even though you shouldn’t talk too much, you do want to be responsive and fully answer the question as best you can.
Badmouthing Past Employers
Your last boss was an idiot? Everyone in the company was a jerk? You hated your job and couldn’t wait to leave?
Even if it’s true don’t say so. Stay Professional. It’s sometimes a smaller world than we think and you don’t know who your interviewer might know, including that boss who is an idiot… You also don’t want the interviewer to think that you might speak that way about his or her company if you leave on terms that aren’t the best.
Don’t Be Cocky
Attitude plays a key role in your interview success. There is a fine balance between confidence and arrogance. Even if you’re putting on a performance to demonstrate your ability, overconfidence is as bad, if not worse, as being too reserved. Ask Questions
At the end of the interview you will usually be given a chance to ask any questions. When asked if they have any questions, most candidates answer, “No.” Wrong answer! It is extremely important to ask questions, not only do they allow the interviewee to acquire more information but they also demonstrate your interest in the position and company.
The best questions come from listening to what is asked during the interview and asking for additional information
Closing
When the Interview is Complete Insure you thank the manager for his time. In most cases the manager will advise you as to when he will make his decision. If he does not define that fact, it is perfectly acceptable to ask. Let the interviewer know that you think you would be a good fit for his or her team and look forward to hearing from him soon. Oracle DBA Interview Questions and Answers – ARCHITECTURE

1. Tell me about yourself? Your role as a DBA? Your Day to Day activities?
2. What is difference between oracle SID and Oracle service name?
Oracle SID is the unique name that uniquely identifies your instance/database where as the service name is the TNS alias can be same or different as SID.
3. What are the steps to install oracle on Linux system? List two kernel parameter that effect oracle installation?
Initially set up disks and kernel parameters, then create oracle user and DBA group, and finally run installer to start the installation process. The SHMMAX & SHMMNI two kernel parameter required to set before installation process.
4. What are bind variables?
With bind variable in SQL, oracle can cache queries in a single time in the SQL cache area. This avoids a hard parse each time, which saves on various locking and latching resource we use to check object existence and so on.
5. What is the difference between data block/extent/segment?
A data block is the smallest unit of logical storage for a database object. As objects grow they take chunks of additional storage that are composed of contiguous data blocks. These groupings of contiguous data blocks are called extents. All the extents that an object takes when grouped together are considered the segment of the database object.
6. What is the difference between PGA and UGA?
When you are running dedicated server then process information stored inside the process global area (PGA) and when you are using shared server then the process information stored inside user global area (UGA).
7. What is SGA? Define structure of shared pool component of SGA?
The system global area is a group of shared memory area that is dedicated to oracle instance. All oracle process uses the SGA to hold information. The SGA is used to store incoming data and internal control information that is needed by the database. You can control the SGA memory by setting the parameter db_cache_size, shared_pool_size and log_buffer.
Shared pool portion contain three major area:
Library cache (parse SQL statement, cursor information and execution plan), data dictionary cache (contain cache, user account information, privilege user information, segments and extent information, data buffer cache for parallel execution message and control structure.
8. What is the difference between SMON and PMON processes?
SMON (System Monitor) performs recovery after instance failure, monitor temporary segments and extents; clean temp segment, coalesce free space. It is mandatory process of DB and starts by default.
PMON (Process Monitor) failed process resources. In shared server architecture monitor and restarts any failed dispatcher or server process. It is mandatory process of DB and starts by default.
9. What is a system change number (SCN)?SCN is a value that is incremented whenever a dirty read occurs.
SCN is incremented whenever a deadlock occurs.
SCN is a value that keeps track of explicit locks.
SCN is a value that is incremented whenever database changes are made.
10. What is the main purpose of ‘CHECKPOINT’ in oracle database? How do you automatically force the oracle to perform a checkpoint?
A checkpoint is a database event, which synchronize the database blocks in memory with the datafiles on disk. It has two main purposes: To establish a data consistency and enable faster database Recovery.
The following are the parameter that will be used by DBA to adjust time or interval of how frequently its checkpoint should occur in database.
LOG_CHECKPOINT_TIMEOUT = 3600; # Every one hour
LOG_CHECKPOINT_INTERVAL = 1000; # number of OS blocks.
11. What happens when we fire SQL statement in Oracle?
First it will check the syntax and semantics in library cache, after that it will create execution plan.
If already data is in buffer cache it will directly return to the client.
If not it will fetch the data from datafiles and write to the database buffer cache after that it will send server and finally server send to the client.
12. What is the use of large pool, which case you need to set the large pool?
You need to set large pool if you are using: MTS (Multi thread server) and RMAN Backups. Large pool prevents RMAN & MTS from competing with other sub system for the same memory. RMAN uses the large pool for backup & restore when you set the DBWR_IO_SLAVES or BACKUP_TAPE_IO_SLAVES parameters to simulate asynchronous I/O. If neither of these parameters is enabled, then Oracle allocates backup buffers from local process memory rather than shared memory. Then there is no use of large pool.
13. What does database do during the mounting process?
While mounting the database oracle reads the data from controlfile which is used for verifying physical database files during sanity check. Background processes are started before mounting the database only.
14. What are logfile states?
“CURRENT” state means that redo records are currently being written to that group. It will be until a log switch occurs. At a time there can be only one redo group current.
If a redo group containing redo’s of a dirty buffer that redo group is said to be ‘ACTIVE’ state. As we know log file keep changes made to the data blocks then data blocks are modified in buffer cache (dirty blocks). These dirty blocks must be written to the disk (RAM to permanent media).
And when a redolog group contains no redo records belonging to a dirty buffer it is in an “INACTIVE” state. These inactive redolog can be overwritten.
One more state ‘UNUSED’ initially when you create new redo log group its log file is empty on that time it is unused. Later it can be any of the above mentioned state.
15. What is log switch?
The point at which oracle ends writing to one online redo log file and begins writing to another is called a log switch. Sometimes you can force the log switch.
ALTER SYSTEM SWITCH LOGFILE;

16. How to check Oracle database version?
SQL> Select * from v$version;
17. Explain Oracle Architecture?
Oracle Instance: a means to access an Oracle database,always opens one and only one database and consists of memory structures and background process.
Oracle server: a DBMS that provides an open, comprehensive, integrated approach to information management,Consists of an Instance and a database.
Oracle database: a collection of data that is treated as a unit,Consists of Datafiles, Control files, Redo log files. (optional param file, passwd file, archived log)
Instance memory Structures:
System Global Area (SGA):
Allocated at instance startup, and is a fundamental component of an Oracle Instance.
SGA Memory structures:
Includes Shared Pool, Database Buffer Cache, Redo Log Buffer among others.
Shared Pool :
Consists of two key performance-related memory structures Library Cache and Data Dictionary Cache.
Library Cache:
Stores information about the most recently used SQL and PL/SQL statements and enables the sharing of commonly used statements.
Data Dictionary Cache :
Stores collection of the most recently used definitions in the database Includes db files, tables, indexes, columns etc. Improves perf. During the parse phase, the server process looks at the data dictionary for information to resolve object names and validate access.
Database Buffer Cache:
Stores copies of data blocks that have been retrieved from the datafiles. Everything done here.
Redo Log Buffer :
Records all changes made to the database data blocks, Primary purpose is recovery. Redo entries contain information to reconstruct or redo changes.
User process:
Started at the time a database User requests connection to the Oracle server. requests interaction with the Oracle server, does not interact directly with the Oracle server.
Server process:
Connects to the Oracle Instance and is Started when a user establishes a session. fulfills calls generated and returns results.
Each server process has its own nonshared PGA when the process is started.
Server Process Parses and run SQL statements issued through the application, Reads necessary data blocks from datafiles on disk into the shared database buffers of the SGA, if the blocks are not already present in the SGA and Return results in such a way that the application can process the information.
In some situations when the application and Oracle Database operate on the same computer, it is possible to combine the user process and corresponding server process into a single process to reduce system overhead.
Program Global Area (PGA):
Memory area used by a single Oracle server process.
Allocated when the server process is started, deallocated when the process is terminated and used by only one process.
Used to process SQL statements and to hold logon and other session information.
Background processes:
Started when an Oracle Instance is started.
Background Processes Maintains and enforces relationships between physical and memory structures
There are two types of database processes:
1. Mandatory background processes
2. Optional background processes
Mandatory background processes:
– DBWn, PMON, CKPT, LGWR, SMON
Optional background processes:
– ARCn, LMDn, RECO, CJQ0, LMON, Snnn, Dnnn, Pnnn, LCKn, QMNn
DBWn writes when:
• Checkpoint occurs
• Dirty buffers reach threshold
• There are no free buffers
• Timeout occurs
• RAC ping request is made
• Tablespace OFFLINE
• Tablespace READ ONLY
• Table DROP or TRUNCATE
• Tablespace BEGIN BACKUP
Log Writer (LGWR) writes:
• At commit
• When 1/3rd full
• When there is 1 MB of redo
• Every 3 seconds
• Before DBWn writes
System Monitor (SMON) Responsibilities:
• Instance recovery
– Rolls forward changes in redo logs
– Opens database for user access
– Rolls back uncommitted transactions
• Coalesces free space
• Deallocates temporary segments.
Process Monitor (PMON) Cleans up after failed processes by:
• Rolling back the transaction
• Releasing locks
• Releasing other resources
• Restarting dead dispatchers
Checkpoint (CKPT) Responsible for:
• Signaling DBWn at checkpoints
• Updating datafile headers with checkpoint information
• Updating control files with checkpoint information
Archiver (ARCn)
• Optional background process
• Automatically archives online redo logs when ARCHIVELOG mode is set
• Preserves the record of all changes made to the database
18. Why do you run orainstRoot and ROOT.SH once you finalize the Installation? orainstRoot.sh needs to be run to change the Permissions and groupname to 770 and to dba.
Root.sh (ORACLE_HOME) location needs to be run to create a ORATAB in /etc/oratab or /opt/var/oratab in Solaris and to copy dbhome, oraenv and coraenv to /usr/local/bin. orainstRoot.sh [root@oracle11g ~]# /u01/app/oraInventory/orainstRoot.sh
Changing permissions of /u01/app/oraInventory to 770.
Changing groupname of /u01/app/oraInventory to dba.
The execution of the script is complete root.sh [root@oracle11g ~]# /u01/app/oracle/product/11.1.0/db_1/root.sh
Running Oracle 11g root.sh script…
The following environment variables are set as:
ORACLE_OWNER= oracle
ORACLE_HOME= /u01/app/oracle/product/11.1.0/db_1
Enter the full pathname of the local bin directory: [/usr/local/bin]:
Copying dbhome to /usr/local/bin …
Copying oraenv to /usr/local/bin …
Copying coraenv to /usr/local/bin …
Creating /etc/oratab file…
Entries will be added to the /etc/oratab file as needed by
Database Configuration Assistant when a database is created
Finished running generic part of root.sh script.
Now product-specific root actions will be performed.
Finished product-specific root actions.
For Oracle installation on unix/linux, we will be prompted to run a script ‘root.sh’ from the oracle inventory directory.this script needs to run the first time only when any oracle product is installed on the server.
It creates the additional directories and sets appropriate ownership and permissions on files for root user.

19. Oracle Database 11g New Feature for DBAs?

1) Automatic Diagnostic Repository [ADR]
2) Database Replay
3) Automatic Memory Tuning
4) Case sensitive password
5) Virtual columns and indexes
6) Interval Partition and System Partition
7) The Result Cache
8) ADDM RAC Enhancements
9) SQL Plan Management and SQL Plan Baselines
10) SQL Access Advisor & Partition Advisor
11) SQL Query Repair Advisor
12) SQL Performance Analyzer (SPA) New
13) DBMS_STATS Enhancements
14) The Result Cache
15) Total Recall (Flashback Data Archive)
Note: The above are only top new features, there are other features as well introduced in 11g which will be included subsequently
20. What is the Difference Between Local Inventory and Global Inventory? What is oraInventory ? oraInventory is repository (directory) which store/records oracle software products & their oracle_homes location on a machine. This Inventory now a days in XML format and called as XML Inventory where as in past it used to be in binary format & called as binary Inventory.
There are basically two kind of inventories,
One is Local Inventory (also called as Oracle Home Inventory) and other is Global Inventory (also called as Central Inventory).

21. What is Global Inventory ?
Global Inventory holds information about Oracle Products on a Machine. These products can be various oracle components like database, oracle application server, collaboration suite, soa suite, forms & reports or discoverer server . This global Inventory location will be determined by file oraInst.loc in /etc (on Linux) or /var/opt/oracle (solaris). If you want to see list of oracle products on machine check for file inventory.xml under ContentsXML in oraInventory Please note if you have multiple global Inventory on machine check all oraInventory directories)
You will see entry like
HOME NAME=”ORA10g_HOME” LOC=”/u01/oracle/10.2.0/db” TYPE=”O” IDX=”1?/

22.What is Local Inventory ?
Inventory inside each Oracle Home is called as local Inventory or oracle_home Inventory. This Inventory holds information to that oracle_home only.

23. What is Oracle Home Inventory?
Oracle home inventory or local inventory is present inside each Oracle home. It only contains information relevant to a particular Oracle home. This file is located in the following location:
$ORACLE_HOME/inventory
It contains the following files and folders:
· Components File
· Home Properties File
· Other Folders

24. Can I have multiple Global Inventory on a machine ?
Quite common questions is that can you have multiple global Inventory and answer is YES you can have multiple global Inventory but if your upgrading or applying patch then change Inventory Pointer oraInst.loc to respective location. If you are following single global Inventory and if you wish to uninstall any software then remove it from Global Inventory as well.
25. What to do if my Global Inventory is corrupted ?
No need to worry if your global Inventory is corrupted, you can recreate global Inventory on machine using Universal Installer and attach already Installed oracle home by option
-attachHome
./runInstaller -silent -attachHome -invPtrLoc $location_to_oraInst.loc
ORACLE_HOME=”Oracle_Home_Location” ORACLE_HOME_NAME=”Oracle_Home_Name”
CLUSTER_NODES=”{}”
26. What is RESULT Cache?
27 .11G Backgroung Processes?
The following process are added in 11g as new background processes.
1 dbrm DB resource manager
2 dia0 Diagnosability process
3 fbda Flashback data archiver process
4 vktm Virtual Timekeeper
5 w000 Space Management Co-ordination process
6 smc0 Space Manager process
NOTE : The above six are mandatory processes.
But 11g has 56 new processes added which can be queried using
28. If any one of these 6 mandatory background processes is killed/not running, the instance will be aborted ?
Background processes are started automatically when the instance is started.
Mandatory background processes are DBWn, LGWR, CKPT, SMON, PMON, and RECO. All other processes are optional, will be invoked if that particular feature is activated.
If any one of these 6 mandatory background processes is killed/not running, the instance will be aborted.
Any issues related to backgroud processes should be monitored and analyzed from the trace files generated and the alert log.
29. What is SGA_TARGET and SGA_MAX_SIZE ?
SGA_MAX_SIZE is the largest amount of memory that will be available for the SGA in the instance and it will be allocated from memory. You do not have to use it all, but it will be potentially wasted if you set it too high and don’t use it. It is not a dynamic parameter. Basically it gives you room for the Oracle instance to grow.
SGA_TARGET is actual memory in use by the current SGA. This parameter is dynamic and can be increased up to the value of SGA_MAX_SIZE.
SGA_MAX_SIZE and SGA_TARGET both are the parameter are used to change the SGA SIZE.
SGA_MAX_SIZE sets the maximum value for sga_target.
SGA_TAGET is 10G feature used to change the sga size dynamically .it specifies the total amount of SGA memory available to an instance. this feature is called Automatic Shared Memory Management. With ASMM, the parameters java_pool_size, shared_pool_size, large_pool_size and db_cache_size are affected.
SGA_MAX_SIZE & SGA_TARGET http://maxwellmiranda.wordpress.com/2009/09/17/sga_max_size-sga_targe/ SGA_MAX_SIZE sets the overall amount of memory the SGA can consume but is not dynamic.
The SGA_MAX_SIZE parameter is the max allowable size to resize the SGA Memory area parameters. If the SGA_TARGET is set to some value then the Automatic Shared Memory Management (ASMM) is enabled, the SGA_TARGET value can be adjusted up to the SGA_MAX_SIZE parameter, not more than SGA_MAX_SIZE parameter value.
I.e. If SGA_MAX_SIZE=4GB and SGA_TARGET=2GB, later period of time, if you want you can resize your SGA_TARGET parameter to the value of SGA_MAX_SIZE i.e. 4GB, you can’t resize the SGA_TARGET value to more than 4GB.
It is significant that SGA_TARGET includes the entire memory for the SGA, in contrast to earlier releases in which memory for the internal and fixed SGA was added to the sum of the configured SGA memory parameters. Thus, SGA_TARGET gives you precise control over the size of the shared memory region allocated by the database. If SGA_TARGET is set to a value greater than SGA_MAX_SIZE at startup, then the latter is bumped up to accommodate SGA_TARGET
Do not dynamically set or unset the SGA_TARGET parameter. This should be set only at startup.
SGA_TARGET is a database initialization parameter (introduced in Oracle 10g) that can be used for automatic SGA memory sizing.
SGA_TARGET provides the following:

§ Single parameter for total SGA size
§ Automatically sizes SGA components
§ Memory is transferred to where most needed
§ Uses workload information
§ Uses internal advisory predictions
§ STATISTICS_LEVEL must be set to TYPICAL
§ SGA_TARGET is dynamic
§ Can be increased till SGA_MAX_SIZE
§ Can be reduced till some component reaches minimum size
§ Change in value of SGA_TARGET affects only automatically sized components

If I keep SGA_TARGET =0 then what will happen ?
Disable automatic SGA tuning by setting sga_target=0
Disable ASMM by setting SGA_TARGET=0 http://www.orafaq.com/wiki/SGA_target SGA_TARGET is a database initialization parameter (introduced in Oracle 10g) that can be used for automatic SGA memory sizing.
Default value 0 (SGA auto tuning is disabled)

30. What happens when you run ALTER DATABASE OPEN RESETLOGS ?
The current online redo logs are archived, the log sequence number is reset to 1, new database incarnation is created, and the online redo logs are given a new time stamp and SCN.
The reason to do the open the database with the resetlogs is that after doing an incomplete recovery , the data files and control files still don’t come to the same point of the redo log files. And as long as the database is not consistent within all the three file-data, redo and control, you can’t open the database. The resetlogs clause would reset the log sequence numbers within the log files and would start them from 0 thus enabling you to open the database but on the cost of losing all what was there in the redo log files.
In what scenarios open resetlogs required ?
An ALTER DATABASE OPEN RESETLOGS statement is required,
1.after incomplete recovery (Point in Time Recovery) or
2.recovery with a backup control file.
3. recovery with a control file recreated with the reset logs option. http://onlineappsdba.com/index.php/2009/09/11/oracle-database-incarnation-open-resetlogs-scn/ http://web.njit.edu/info/limpid/DOC/backup.102/b14191/osrecov009.htm
Whenever you perform incomplete recovery or recovery with a backup control file, you must reset the online logs when you open the database. The new version of the reset database is called a new incarnation..
31. Difference between RESETLOGS and NORESETLOGS ? http://oracleappstechnology.blogspot.in/2008/05/difference-between-resetlogs-and.html After recover database operation, open the database with: ALTER DATABASE OPEN [NO]RESETLOGS
NORESETLOGS:
The NORESETLOGS option does not clear the redo log files during startup and the online redo logs to be used for recovery. Only used in scenario where MANUAL RECOVERY is started, CANCEL is used, and then RECOVER DATABASE is started.
RESETLOGS:
CAUTION: Never use RESETLOGS unless necessary.
Once RESETLOGS is used then the redo log files cannot be used and any completed transactions in those redo logs are lost!!
Before using the RESETLOGS option take an offline backup of the database.
32. What is SCN (System Change Number) ?
The system change number (SCN) is an ever-increasing value that uniquely identifies a committed version of the database at a point in time. Every time a user commits a transaction Oracle records a new SCN in redo logs.
Oracle uses SCNs in control files datafile headers and redo records. Every redo log file has both a log sequence number and low and high SCN. The low SCN records the lowest SCN recorded in the log file while the high SCN records the highest SCN in the log file.
33. What is Database Incarnation ?
Database incarnation is effectively a new “version” of the database that happens when you reset the online redo logs using “alter database open resetlogs;”.
Database incarnation falls into following category Current, Parent, Ancestor and Sibling
i) Current Incarnation : The database incarnation in which the database is currently generating redo. ii) Parent Incarnation : The database incarnation from which the current incarnation branched following an OPEN RESETLOGS operation. iii) Ancestor Incarnation : The parent of the parent incarnation is an ancestor incarnation. Any parent of an ancestor incarnation is also an ancestor incarnation. iv) Sibling Incarnation : Two incarnations that share a common ancestor are sibling incarnations if neither one is an ancestor of the other.
34. How to view Database Incarnation history of Database ?
Using SQL> select * from v$database_incarnation;
Using RMAN>LIST INCARNATION;
However, you can use the RESET DATABASE TO INCARNATION command to specify that SCNs are to be interpreted in the frame of reference of another incarnation.
•For example my current database INCARNATION is 3 and now I have used
FLASHBACK DATABASE TO SCN 3000;then SCN 3000 will be search in current incarnation which is 3. However if I want to get back to SCN 3000 of INCARNATION 2 then I have to use,
RMAN> RESET DATABASE TO INCARNATION 2;
RMAN> RECOVER DATABASE TO SCN 3000;

1. What is an instance?
SGA + background processes.

2. What is SGA?
System/Shared Global Area.

3. What is PGA (or) what is pga_aggregate_target?
Programmable Global Area.

4. What are new memory parameters in Oracle 10g?
SGA_TARGET PGA_TARGET

5. What are new memory parameters in Oracle 11g?
MEMORY_TARGET

6. What are the mandatory background processes?
DBWR LGWR SMON PMON CKPT RECO.

7. What are the optional background processes?
ARCH, MMAN, MMNL, MMON, CTWR, ASMB, RBAL, ARBx etc.

8. What are the new background processes in Oracle 10g?
MMAN MMON MMNL CTWR ASMB RBAL ARBx

9. What are the new features in Oracle 9i? http://satya-dba.blogspot.com/2009/01/whats-new-in-9i.html 10. What are the new features in Oracle 10g? http://satya-dba.blogspot.com/2009/01/whats-new-in-10g.html 11. What are the new features in Oracle 11g? http://satya-dba.blogspot.com/2009/01/whats-new-in-11g.html 12. What are the new features in Oracle 11g R2? http://satya-dba.blogspot.com/2009/09/whats-new-in-11g-release-2.html 13. What are the new features in Oracle 12c? http://satya-dba.blogspot.com/2012/10/new-features-in-oracle-database-12c.html 14. What process will get data from datafiles to DB cache?
Server process

15. What background process will writes data to datafiles?
DBWR

16. What background process will write undo data?
DBWR

17. What are physical components of Oracle database?
Oracle database is comprised of three types of files. One or more datafiles, two or more redo log files, and one or more control files. Password file and parameter file also come under physical components.

18. What are logical components of Oracle database?
Blocks, Extents, Segments, Tablespaces.

19. What is segment space management?
LMTS and DMTS.

20. What is extent management? What are the differences between LMTS and DMTS?
Auto and Manual.
Tablespaces that record extent allocation in the dictionary are called dictionary managed tablespaces, and tablespaces that record extent allocation in the tablespace header are called locally managed tablespaces.
21. What is a datafile?
Every Oracle database has one or more physical datafiles. Datafiles contain all the database data. The data of logical database structures such as tables and indexes is physically stored in the datafiles allocated for a database.

22. What are the contents of control file?
Database name, SCN, LSN, datafile locations, redolog locations, archive mode, DB Creation Time, RMAN Backup & Recovery Details, Flashback mode.

23. What is the use of redo log files?

24. What are the uses of undo tablespace or redo segments?

25. How undo tablespace can guarantee retain of required undo data?
Alter tablespace undo_ts retention guarantee;

26. What is ORA-01555 - snapshot too old error and how do you avoid it?

27. What is the use/size of temporary tablespace?

28. What is the use of password file?

29. How to create password file?
$ orapwd file=orapwSID password=sys_password force=y nosysdba=y

30. How many types of indexes are there?
Clustered and Non-Clustered

1.B-Tree index
2.Bitmap index
3.Unique index
4.Function based index

Implicit index and explicit index.
Explicit indexes are again of many types like simple index, unique index, Bitmap index, Functional index, Organisational index, cluster index.

31. What is bitmap index & when it’ll be used?
Bitmap indexes are preferred in Data warehousing environment.
Preferred when cardinality is low.

32. What is B-tree index & when it’ll be used?
B-tree indexes are preferred in OLTP environment.
Preferred when cardinality is high.

33. How you will find out fragmentation of index?
AUTO_SPACE_ADVISOR_JOB will run in daily maintenance window and report fragmented indexes/Tables.

analyze index validate structure;
This populates the table ‘index_stats’. It should be noted that this table contains only one row and therefore only one index can be analysed at a time.

An index should be considered for rebuilding under any of the following conditions:
* The percentage of deleted rows exceeds 30% of the total, i.e. if del_lf_rows / lf_rows > 0.3.
* If the ‘HEIGHT’ is greater than 4.
* If the number of rows in the index (‘LF_ROWS’) is significantly smaller than ‘LF_BLKS’ this can indicate a large number of deletes, indicating that the index should be rebuilt.

34. What is the difference between delete and truncate?
Truncate will release the space. Delete won’t.
Delete can be used to delete some records. Truncate can’t.
Delete can be rollbacked.
Delete will generate undo (Delete command will log the data changes in the log file where as the truncate will simply remove the data without it. Hence data removed by Delete command can be rolled back but not the data removed by TRUNCATE).
Truncate is a DDL statement whereas DELETE is a DML statement.
Truncate is faster than delete.

35. What's the difference between a primary key and a unique key?
Both primary key and unique enforce uniqueness of the column on which they are defined. But by default primary key creates a clustered index on the column, where unique key creates a nonclustered index by default. Primary key doesn't allow NULLs, but unique key allows one NULL only.

36. What is the difference between schema and user?
Schema is collection of user’s objects.

37. What is the difference between SYSDBA, SYSOPER and SYSASM?
SYSOPER can’t create and drop database.
SYSOPER can’t do incomplete recovery.
SYSOPER can’t change character set.
SYSOPER can’t CREATE DISKGROUP, ADD/DROP/RESIZE DISK

SYSASM can do anything SYSDBA can do.

38. What is the difference between SYS and SYSTEM?
SYSTEM can’t shutdown the database.
SYSTEM can’t create another SYSTEM, but SYS can create another SYS or SYSTEM.

39. How to improve sqlldr (SQL*Loader) performance?

40. What is the difference between view and materialized view?
View is logical, will store only the query, and will always gets latest data.
Mview is physical, will store the data, and may not get latest data.

41. What are materialized view refresh types and which is default?
Complete, fast, force(default)

42. How fast refresh happens?

43. How to find out when was a materialized view refreshed?
Query dba_mviews or dba_mview_analysis or dba_mview_refresh_times
SQL> select MVIEW_NAME, to_char(LAST_REFRESH_DATE,'YYYY-MM-DD HH24:MI:SS') from dba_mviews;
(or)
SQL> select NAME, to_char(LAST_REFRESH,'YYYY-MM-DD HH24:MI:SS') from dba_mview_refresh_times;
(or)
SQL> select MVIEW_NAME, to_char(LAST_REFRESH_DATE,'YYYY-MM-DD HH24:MI:SS') from dba_mview_analysis;

44. What is materialized view log (type)?

45. What is atomic refresh in mviews?
From Oracle 10g, complete refresh of single materialized view can do delete instead of truncate. To force the refresh to do truncate instead of delete, parameter ATOMIC_REFRESH must be set to false.

ATOMIC_REFRESH = FALSE, mview will be truncated and whole data will be inserted. The refresh will go faster, and no undo will be generated.
ATOMIC_REFRESH = TRUE (default), mview will be deleted and whole data will be inserted. Undo will be generated. We will have access at all times even while it is being refreshed.

SQL> EXEC DBMS_MVIEW.REFRESH('mv_emp', 'C', atomic_refresh=FALSE);

46. How to find out whether database/tablespace/datafile is in backup mode or not?
Query V$BACKUP view.

47. What is row chaining?
If the row is too large to fit into an empty data block in this case the oracle stores the data for the row in a chain of one or more data blocks. Can occur when the row is inserted.

48. What is row migration?
An update statement increases the amount of data in a row so that the row no longer fits in its data blocks. Now the oracle tries to find another free block with enough space to hold the entire row if such a block is available oracle moves entire row to new block.

49. What are different types of partitions?
With Oracle8, Range partitioning (on single column) was introduced.
With Oracle8i, Hash and Composite(Range-Hash) partitioning was introduced.
With Oracle9i, List partitioning and Composite(Range-List) partitioning was introduced.
With Oracle 11g, Interval partitioning, REFerence partitioning, Virtual column based partitioning, System partitioning and Composite partitioning [Range-Range, List-List, List-Range, List-Hash, Interval-Range, Interval-List, Interval-Interval] was introduced.

50. What is local partitioned index and global partitioned index?
A local index is an index on a partitioned table which is partitioned in the exact same manner as the underlying partitioned table. Each partition of a local index corresponds to one and only one partition of the underlying table.
A global partitioned index is an index on a partitioned or non partitioned tables which are partitioned using a different partitioning key from the table and can have different number of partitions. Global partitioned indexes can only be partitioned using range partitioning.

51. How you will recover if you lost one/all control file(s)?

52. Why more archivelogs are generated, when database is begin backup mode?
During begin backup mode datafile headers get freezed and as result row information cannot be retrieved as a result the entire block is copied to redo logs as a result more redo generated and more log switch and in turn more archive logs. Normally only deltas (change vectors) are logged to the redo logs. When in backup mode, Oracle will write complete changed blocks to the redo log files.

Mainly to overcome fractured blocks. Most of the cases Oracle block size is equal to or a multiple of the operating system block size.

e.g. Consider Oracle blocksize is 2k and OSBlocksize is 4k. so each OS Block is comprised of 2 Oracle Blocks. Now you are doing an update when your db is in backup mode. An Oracle Block is updating and at the same time backup is happening on the OS block which is having this particular DB block. Backup will not be consistent since the one part of the block is being updated and at the same time it is copied to the backup location. In this case we will have a fractured block, so as to avoid this Oracle will copy the whole OS block to redo logfile which can be used for recovery. Because of this redo generation is more.

53. What UNIX parameters you will set while Oracle installation? shmmax, shmmni, shmall, sem,

54. What is the use of inittrans and maxtrans in table definition?

55. What are differences between dbms_job and dbms_schedular?
Through dbms_schedular we can schedule OS level jobs also.

56. What are differences between dbms_schedular and cron jobs?
Through dbms_schedular we can schedule database jobs, through cron we can’t set.

57. Difference between CPU & PSU patches?
CPU - Critical Patch Update - includes only Security related patches.
PSU - Patch Set Update - includes CPU + other patches deemed important enough to be released prior to a minor (or major) version release.

58. What you will do if (local) inventory corrupted [or] opatch lsinventory is giving error?

59. What are the entries/location of oraInst.loc?
/etc/oraInst.loc is pointer to central/local Oracle Inventory.

60. What is the difference between central/global inventory and local inventory?

61. What is the use of root.sh & oraInstRoot.sh?
Ans:
Changes ownership & permissions of oraInventory
Creating oratab file in the /etc directory
In RAC, starts the clusterware stack

62. What is transportable tablespace (and across platforms)?

63. How can you transport tablespaces across platforms with different endian formats?
Ans:
RMAN

64. What is xtss (cross platform transportable tablespace)?

65. What is the difference between restore point & guaranteed restore point?

66. What is the difference between 10g/11g OEM Grid control and 12c Cloud control?

67. What are the components of Grid control?
Ans:
OMS (Oracle Management Server)
OMR (Oracle Management Repository)
OEM Agent

68. What are the new features of 12c Cloud control?

69. How to find if your Oracle database is 32 bit or 64 bit?
Ans:
execute the command "file $ORACLE_HOME/bin/oracle", you should see output like /u01/db/bin/oracle: ELF 64-bit MSB executable SPARCV9 Version 1

means you are on 64 bit oracle.

If your oracle is 32 bit you should see output like below oracle: ELF 32-bit MSB executable SPARC Version 1

70. How to find opatch Version ?
Ans:
opatch is utility to apply database patch, In order to find opatch version execute"$ORACLE_HOME/OPatch/opatch version"

What is difference between oracle SID and Oracle service name?
Oracle SID is the unique name that uniquely identifies your instance/database where as the service name is the TNS alias can be same or different as SID.

What are the steps to install oracle on Linux system? List two kernel parameter that effect oracle installation?
Initially set up disks and kernel parameters, then create oracle user and DBA group, and finally run installer to start the installation process. The SHMMAX & SHMMNI two kernel parameter required to set before installation process.

What are bind variables?
With bind variable in SQL, oracle can cache queries in a single time in the SQL cache area. This avoids a hard parse each time, which saves on various locking and latching resource we use to check object existence and so on.

What is the difference between data block/extent/segment?
A data block is the smallest unit of logical storage for a database object. As objects grow they take chunks of additional storage that are composed of contiguous data blocks. These groupings of contiguous data blocks are called extents. All the extents that an object takes when grouped together are considered the segment of the database object.

What is the difference between PGA and UGA?
When you are running dedicated server then process information stored inside the process global area (PGA) and when you are using shared server then the process information stored inside user global area (UGA).

What is SGA? Define structure of shared pool component of SGA?
The system global area is a group of shared memory area that is dedicated to oracle instance. All oracle process uses the SGA to hold information. The SGA is used to store incoming data and internal control information that is needed by the database. You can control the SGA memory by setting the parameter db_cache_size, shared_pool_size and log_buffer.
Shared pool portion contain three major area:
Library cache (parse SQL statement, cursor information and execution plan), data dictionary cache (contain cache, user account information, privilege user information, segments and extent information, data buffer cache for parallel execution message and control structure.

What is the difference between SMON and PMON processes?
SMON (System Monitor) performs recovery after instance failure, monitor temporary segments and extents; clean temp segment, coalesce free space. It is mandatory process of DB and starts by default.
PMON (Process Monitor) failed process resources. In shared server architecture monitor and restarts any failed dispatcher or server process. It is mandatory process of DB and starts by default.

What is a system change number (SCN)?SCN is a value that is incremented whenever a dirty read occurs.
SCN is incremented whenever a deadlock occurs.
SCN is a value that keeps track of explicit locks.
SCN is a value that is incremented whenever database changes are made.

What is the main purpose of ‘CHECKPOINT’ in oracle database? How do you automatically force the oracle to perform a checkpoint? A checkpoint is a database event, which synchronize the database blocks in memory with the datafiles on disk. It has two main purposes: To establish a data consistency and enable faster database Recovery.

The following are the parameter that will be used by DBA to adjust time or interval of how frequently its checkpoint should occur in database.
LOG_CHECKPOINT_TIMEOUT = 3600; # Every one hour
LOG_CHECKPOINT_INTERVAL = 1000; # number of OS blocks.

What happens when we fire SQL statement in Oracle?
First it will check the syntax and semantics in library cache, after that it will create execution plan.
If already data is in buffer cache it will directly return to the client.
If not it will fetch the data from datafiles and write to the database buffer cache after that it will send server and finally server send to the client.

What is the use of large pool, which case you need to set the large pool?
You need to set large pool if you are using: MTS (Multi thread server) and RMAN Backups. Large pool prevents RMAN & MTS from competing with other sub system for the same memory. RMAN uses the large pool for backup & restore when you set the DBWR_IO_SLAVES or BACKUP_TAPE_IO_SLAVES parameters to simulate asynchronous I/O. If neither of these parameters is enabled, then Oracle allocates backup buffers from local process memory rather than shared memory. Then there is no use of large pool.

What does database do during the mounting process?
While mounting the database oracle reads the data from controlfile which is used for verifying physical database files during sanity check. Background processes are started before mounting the database only.

What are logfile states?
“CURRENT” state means that redo records are currently being written to that group. It will be until a log switch occurs. At a time there can be only one redo group current.
If a redo group containing redo’s of a dirty buffer that redo group is said to be ‘ACTIVE’ state. As we know log file keep changes made to the data blocks then data blocks are modified in buffer cache (dirty blocks). These dirty blocks must be written to the disk (RAM to permanent media).
And when a redolog group contains no redo records belonging to a dirty buffer it is in an "INACTIVE" state. These inactive redolog can be overwritten.
One more state ‘UNUSED’ initially when you create new redo log group its log file is empty on that time it is unused. Later it can be any of the above mentioned state.

What is log switch?
The point at which oracle ends writing to one online redo log file and begins writing to another is called a log switch. Sometimes you can force the log switch.
ALTER SYSTEM SWITCH LOGFILE;
How to check Oracle database version?
SQL> Select * from v$version;

Explain Oracle Architecture?
Oracle Instance: a means to access an Oracle database,always opens one and only one database and consists of memory structures and background process.
Oracle server: a DBMS that provides an open, comprehensive, integrated approach to information management,Consists of an Instance and a database.
Oracle database: a collection of data that is treated as a unit,Consists of Datafiles, Control files, Redo log files. (optional param file, passwd file, archived log)

Instance memory Structures:

System Global Area (SGA):
Allocated at instance startup, and is a fundamental component of an Oracle Instance.

SGA Memory structures:
Includes Shared Pool, Database Buffer Cache, Redo Log Buffer among others.
Shared Pool :
Consists of two key performance-related memory structures Library Cache and Data Dictionary Cache.
Library Cache:
Stores information about the most recently used SQL and PL/SQL statements and enables the sharing of commonly used statements.
Data Dictionary Cache :
Stores collection of the most recently used definitions in the database Includes db files, tables, indexes, columns etc. Improves perf. During the parse phase, the server process looks at the data dictionary for information to resolve object names and validate access.
Database Buffer Cache:
Stores copies of data blocks that have been retrieved from the datafiles. Everything done here.
Redo Log Buffer :
Records all changes made to the database data blocks, Primary purpose is recovery. Redo entries contain information to reconstruct or redo changes.
User process:
Started at the time a database User requests connection to the Oracle server. requests interaction with the Oracle server, does not interact directly with the Oracle server.
Server process:
Connects to the Oracle Instance and is Started when a user establishes a session. fulfills calls generated and returns results.
Each server process has its own nonshared PGA when the process is started.
Server Process Parses and run SQL statements issued through the application, Reads necessary data blocks from datafiles on disk into the shared database buffers of the SGA, if the blocks are not already present in the SGA and Return results in such a way that the application can process the information.
In some situations when the application and Oracle Database operate on the same computer, it is possible to combine the user process and corresponding server process into a single process to reduce system overhead.
Program Global Area (PGA):
Memory area used by a single Oracle server process.
Allocated when the server process is started, deallocated when the process is terminated and used by only one process.
Used to process SQL statements and to hold logon and other session information.

Background processes:
Started when an Oracle Instance is started.
Background Processes Maintains and enforces relationships between physical and memory structures
There are two types of database processes: 1. Mandatory background processes 2. Optional background processes
Mandatory background processes:
– DBWn, PMON, CKPT, LGWR, SMON
Optional background processes:
– ARCn, LMDn, RECO, CJQ0, LMON, Snnn, Dnnn, Pnnn, LCKn, QMNn
DBWn writes when:
• Checkpoint occurs
• Dirty buffers reach threshold
• There are no free buffers
• Timeout occurs
• RAC ping request is made
• Tablespace OFFLINE
• Tablespace READ ONLY
• Table DROP or TRUNCATE
• Tablespace BEGIN BACKUP
Log Writer (LGWR) writes:
• At commit
• When 1/3rd full
• When there is 1 MB of redo
• Every 3 seconds
• Before DBWn writes

System Monitor (SMON) Responsibilities:
• Instance recovery
– Rolls forward changes in redo logs
– Opens database for user access
– Rolls back uncommitted transactions
• Coalesces free space
• Deallocates temporary segments.
Process Monitor (PMON) Cleans up after failed processes by:
• Rolling back the transaction
• Releasing locks
• Releasing other resources
• Restarting dead dispatchers
Checkpoint (CKPT) Responsible for:
• Signaling DBWn at checkpoints
• Updating datafile headers with checkpoint information
• Updating control files with checkpoint information
Archiver (ARCn)
• Optional background process
• Automatically archives online redo logs when ARCHIVELOG mode is set
• Preserves the record of all changes made to the database

Why do you run orainstRoot and ROOT.SH once you finalize the Installation? orainstRoot.sh needs to be run to change the Permissions and groupname to 770 and to dba.
Root.sh (ORACLE_HOME) location needs to be run to create a ORATAB in /etc/oratab or /opt/var/oratab in Solaris and to copy dbhome, oraenv and coraenv to /usr/local/bin. orainstRoot.sh [root@oracle11g ~]# /u01/app/oraInventory/orainstRoot.sh
Changing permissions of /u01/app/oraInventory to 770.
Changing groupname of /u01/app/oraInventory to dba.
The execution of the script is complete root.sh [root@oracle11g ~]# /u01/app/oracle/product/11.1.0/db_1/root.sh
Running Oracle 11g root.sh script...
The following environment variables are set as:
ORACLE_OWNER= oracle
ORACLE_HOME= /u01/app/oracle/product/11.1.0/db_1
Enter the full pathname of the local bin directory: [/usr/local/bin]:
Copying dbhome to /usr/local/bin ...
Copying oraenv to /usr/local/bin ...
Copying coraenv to /usr/local/bin ...
Creating /etc/oratab file...
Entries will be added to the /etc/oratab file as needed by
Database Configuration Assistant when a database is created
Finished running generic part of root.sh script.
Now product-specific root actions will be performed.
Finished product-specific root actions.
For Oracle installation on unix/linux, we will be prompted to run a script 'root.sh' from the oracle inventory directory.this script needs to run the first time only when any oracle product is installed on the server.
It creates the additional directories and sets appropriate ownership and permissions on files for root user. File type | Extension | Default location (when created with OMF) | Pfile : | ORA | C:\oracle\product\10.2.0\admin\orcl\pfile | Spfile: | ORA | C:\oracle\product\10.2.0\db_1\database | Control file: | CTL | C:\oracle\product\10.2.0\oradata\orcl | Redo log file: | LOG | C:\oracle\product\10.2.0\oradata\orcl | Archive log file: | LOG | C:\oracle\product\10.2.0\flash_recovery_area\ORCL\ARCHIVELOG | Data file: | DBF | C:\oracle\product\10.2.0\oradata\orcl | Alert log files: | LOG | C:\oracle\product\10.2.0\admin\orcl\adump | Trace log files: | TRC | C:\oracle\product\10.2.0\admin\orcl\udump|bdump|cdump | Password file: | ORA | C:\oracle\product\10.2.0\db_1\database |

Oracle Database 11g New Feature for DBAs?
1) Automatic Diagnostic Repository [ADR]
2) Database Replay
3) Automatic Memory Tuning
4) Case sensitive password
5) Virtual columns and indexes
6) Interval Partition and System Partition
7) The Result Cache
8) ADDM RAC Enhancements
9) SQL Plan Management and SQL Plan Baselines
10) SQL Access Advisor & Partition Advisor
11) SQL Query Repair Advisor
12) SQL Performance Analyzer (SPA) New
13) DBMS_STATS Enhancements
14) The Result Cache
15) Total Recall (Flashback Data Archive)
Note: The above are only top new features, there are other features as well introduced in 11g which will be included subsequently

What is the Difference Between Local Inventory and Global Inventory?
What is oraInventory ? oraInventory is repository (directory) which store/records oracle software products & their oracle_homes location on a machine. This Inventory now a days in XML format and called as XML Inventory where as in past it used to be in binary format & called as binary Inventory.
There are basically two kind of inventories,
One is Local Inventory (also called as Oracle Home Inventory) and other is Global Inventory (also called as Central Inventory).
What is Global Inventory?
Global Inventory holds information about Oracle Products on a Machine. These products can be various oracle components like database, oracle application server, collaboration suite, soa suite, forms & reports or discoverer server. This global Inventory location will be determined by file oraInst.loc in /etc (on Linux) or /var/opt/oracle (solaris). If you want to see list of oracle products on machine check for file inventory.xml under ContentsXML in oraInventory please note if you have multiple global Inventory on machine check all oraInventory directories)
You will see entry like
HOME NAME=”ORA10g_HOME” LOC=”/u01/oracle/10.2.0/db” TYPE=”O” IDX=”1?/
What is Local Inventory?
Inventory inside each Oracle Home is called as local Inventory or oracle_home Inventory. This Inventory holds information to that oracle_home only.
What is Oracle Home Inventory?
Oracle home inventory or local inventory is present inside each Oracle home. It only contains information relevant to a particular Oracle home. This file is located in the following location:
$ORACLE_HOME/inventory
It contains the following files and folders:
· Components File
· Home Properties File
· Other Folders
Can I have multiple Global Inventory on a machine?
Quite common questions is that can you have multiple global Inventory and answer is YES you can have multiple global Inventory but if your upgrading or applying patch then change Inventory Pointer oraInst.loc to respective location. If you are following single global Inventory and if you wish to uninstall any software then remove it from Global Inventory as well.

What to do if my Global Inventory is corrupted ?
No need to worry if your global Inventory is corrupted, you can recreate global Inventory on machine using Universal Installer and attach already Installed oracle home by option
-attachHome
./runInstaller -silent -attachHome -invPtrLoc $location_to_oraInst.loc
ORACLE_HOME=”Oracle_Home_Location” ORACLE_HOME_NAME=”Oracle_Home_Name”
CLUSTER_NODES=”{}”

What is RESULT Cache?

11G Backgroung Processes?
The following process are added in 11g as new background processes.
1 dbrm DB resource manager
2 dia0 Diagnosability process
3 fbda Flashback data archiver process
4 vktm Virtual Timekeeper
5 w000 Space Management Co-ordination process
6 smc0 Space Manager process
NOTE : The above six are mandatory processes.
But 11g has 56 new processes added which can be queried using

If any one of these 6 mandatory background processes is killed/not running, the instance will be aborted ?
Background processes are started automatically when the instance is started.
Mandatory background processes are DBWn, LGWR, CKPT, SMON, PMON, and RECO. All other processes are optional, will be invoked if that particular feature is activated.
If any one of these 6 mandatory background processes is killed/not running, the instance will be aborted.
Any issues related to backgroud processes should be monitored and analyzed from the trace files generated and the alert log.

Literal Vs. Bind Variables?

Select * from emp where dept=10; what level should i configure for better performance Where Clause .... Literal or Bind Variables? Expalin?

What is a Baseline?

Incarnation? Explain in detail? Where the incarnation information will be stored?

Hard Parse Vs. Soft Parse?

What is semaphores, semaphores?

What is latch?

What is Enqueue?
What is SGA_TARGET and SGA_MAX_SIZE ?
SGA_MAX_SIZE is the largest amount of memory that will be available for the SGA in the instance and it will be allocated from memory. You do not have to use it all, but it will be potentially wasted if you set it too high and don't use it. It is not a dynamic parameter. Basically it gives you room for the Oracle instance to grow.
SGA_TARGET is actual memory in use by the current SGA. This parameter is dynamic and can be increased up to the value of SGA_MAX_SIZE.
SGA_MAX_SIZE and SGA_TARGET both are the parameter are used to change the SGA SIZE.
SGA_MAX_SIZE sets the maximum value for sga_target.
SGA_TAGET is 10G feature used to change the sga size dynamically .it specifies the total amount of SGA memory available to an instance. this feature is called Automatic Shared Memory Management. With ASMM, the parameters java_pool_size, shared_pool_size, large_pool_size and db_cache_size are affected.

SGA_MAX_SIZE & SGA_TARGET http://maxwellmiranda.wordpress.com/2009/09/17/sga_max_size-sga_targe/ SGA_MAX_SIZE sets the overall amount of memory the SGA can consume but is not dynamic.
The SGA_MAX_SIZE parameter is the max allowable size to resize the SGA Memory area parameters. If the SGA_TARGET is set to some value then the Automatic Shared Memory Management (ASMM) is enabled, the SGA_TARGET value can be adjusted up to the SGA_MAX_SIZE parameter, not more than SGA_MAX_SIZE parameter value.
I.e. If SGA_MAX_SIZE=4GB and SGA_TARGET=2GB, later period of time, if you want you can resize your SGA_TARGET parameter to the value of SGA_MAX_SIZE i.e. 4GB, you can’t resize the SGA_TARGET value to more than 4GB.
It is significant that SGA_TARGET includes the entire memory for the SGA, in contrast to earlier releases in which memory for the internal and fixed SGA was added to the sum of the configured SGA memory parameters. Thus, SGA_TARGET gives you precise control over the size of the shared memory region allocated by the database. If SGA_TARGET is set to a value greater than SGA_MAX_SIZE at startup, then the latter is bumped up to accommodate SGA_TARGET
Do not dynamically set or unset the SGA_TARGET parameter. This should be set only at startup.
SGA_TARGET is a database initialization parameter (introduced in Oracle 10g) that can be used for automatic SGA memory sizing.
SGA_TARGET provides the following:
§ Single parameter for total SGA size
§ Automatically sizes SGA components
§ Memory is transferred to where most needed
§ Uses workload information
§ Uses internal advisory predictions
§ STATISTICS_LEVEL must be set to TYPICAL
§ SGA_TARGET is dynamic
§ Can be increased till SGA_MAX_SIZE
§ Can be reduced till some component reaches minimum size
§ Change in value of SGA_TARGET affects only automatically sized components
If I keep SGA_TARGET =0 then what will happen?
Disable automatic SGA tuning by setting sga_target=0
Disable ASMM by setting SGA_TARGET=0 http://www.orafaq.com/wiki/SGA_target SGA_TARGET is a database initialization parameter (introduced in Oracle 10g) that can be used for automatic SGA memory sizing.
Default value 0 (SGA auto tuning is disabled)
What happens when you run ALTER DATABASE OPEN RESETLOGS ?
The current online redo logs are archived, the log sequence number is reset to 1, new database incarnation is created, and the online redo logs are given a new time stamp and SCN.
The reason to do the open the database with the resetlogs is that after doing an incomplete recovery , the data files and control files still don't come to the same point of the redo log files. And as long as the database is not consistent within all the three file-data, redo and control, you can't open the database. The resetlogs clause would reset the log sequence numbers within the log files and would start them from 0 thus enabling you to open the database but on the cost of losing all what was there in the redo log files.
In what scenarios open resetlogs required ?
An ALTER DATABASE OPEN RESETLOGS statement is required,
1.after incomplete recovery (Point in Time Recovery) or
2.recovery with a backup control file.
3. recovery with a control file recreated with the reset logs option. http://onlineappsdba.com/index.php/2009/09/11/oracle-database-incarnation-open-resetlogs-scn/ http://web.njit.edu/info/limpid/DOC/backup.102/b14191/osrecov009.htm
Whenever you perform incomplete recovery or recovery with a backup control file, you must reset the online logs when you open the database. The new version of the reset database is called a new incarnation..

Difference between RESETLOGS and NORESETLOGS ? http://oracleappstechnology.blogspot.in/2008/05/difference-between-resetlogs-and.html After recover database operation, open the database with: ALTER DATABASE OPEN [NO]RESETLOGS
NORESETLOGS:
The NORESETLOGS option does not clear the redo log files during startup and the online redo logs to be used for recovery. Only used in scenario where MANUAL RECOVERY is started, CANCEL is used, and then RECOVER DATABASE is started.
RESETLOGS:
CAUTION: Never use RESETLOGS unless necessary.
Once RESETLOGS is used then the redo log files cannot be used and any completed transactions in those redo logs are lost!!
Before using the RESETLOGS option take an offline backup of the database.

What is SCN (System Change Number) ?
The system change number (SCN) is an ever-increasing value that uniquely identifies a committed version of the database at a point in time. Every time a user commits a transaction Oracle records a new SCN in redo logs.
Oracle uses SCNs in control files datafile headers and redo records. Every redo log file has both a log sequence number and low and high SCN. The low SCN records the lowest SCN recorded in the log file while the high SCN records the highest SCN in the log file.

What is Database Incarnation ?
Database incarnation is effectively a new “version” of the database that happens when you reset the online redo logs using “alter database open resetlogs;”.
Database incarnation falls into following category Current, Parent, Ancestor and Sibling
i) Current Incarnation : The database incarnation in which the database is currently generating redo. ii) Parent Incarnation : The database incarnation from which the current incarnation branched following an OPEN RESETLOGS operation. iii) Ancestor Incarnation : The parent of the parent incarnation is an ancestor incarnation. Any parent of an ancestor incarnation is also an ancestor incarnation. iv) Sibling Incarnation : Two incarnations that share a common ancestor are sibling incarnations if neither one is an ancestor of the other.

How to view Database Incarnation history of Database ?
Using SQL> select * from v$database_incarnation;
Using RMAN>LIST INCARNATION;
However, you can use the RESET DATABASE TO INCARNATION command to specify that SCNs are to be interpreted in the frame of reference of another incarnation.
•For example my current database INCARNATION is 3 and now I have used
FLASHBACK DATABASE TO SCN 3000;then SCN 3000 will be search in current incarnation which is 3. However if I want to get back to SCN 3000 of INCARNATION 2 then I have to use,
RMAN> RESET DATABASE TO INCARNATION 2;
RMAN> RECOVER DATABASE TO SCN 3000;

http://rajeevjhaoracle.wordpress.com/2012/01/12/pfile-and-spfile-initialization-files-in-oracle/
What are new background processes are there in 10g and 11g http://oracleinstance.blogspot.in/2009/11/oracle-background-processes.html http://www.dba-oracle.com/concepts/background_processes_concepts.htm

SENIOR ORACLE DBA INTERVIEW QUESTIONS

1. Explain the difference between a hot backup and a cold backup and the benefits associated with each.
A hot backup is basically taking a backup of the database while it is still up and running and it must be in archive log mode. A cold backup is taking a backup of the database while it is shut down and does not require being in archive log mode. The benefit of taking a hot backup is that the database is still available for use while the backup is occurring and you can recover the database to any point in time. The benefit of taking a cold backup is that it is typically easier to administer the backup and recovery process. In addition, since you are taking cold backups the database does not require being in archive log mode and thus there will be a slight performance gain as the database is not cutting archive logs to disk.
2. You have just had to restore from backup and do not have any control files. How would you go about bringing up this database?
I would create a text based backup control file, stipulating where on disk all the data files where and then issue the recover command with the using backup control file clause.
3. How do you switch from an init.ora file to a spfile?
Issue the create spfile from pfile command.
4. Explain the difference between a data block, an extent and a segment.
A data block is the smallest unit of logical storage for a database object. As objects grow they take chunks of additional storage that are composed of contiguous data blocks. These groupings of contiguous data blocks are called extents. All the extents that an object takes when grouped together are considered the segment of the database object.
5. Give two examples of how you might determine the structure of the table DEPT.
Use the describe command or use the dbms_metadata.get_ddl package.
6. Where would you look for errors from the database engine? In the alert log.
7. Compare and contrast TRUNCATE and DELETE for a table.
Both the truncate and delete command have the desired outcome of getting rid of all the rows in a table. The difference between the two is that the truncate command is a DDL operation and just moves the high water mark and produces a now rollback. The delete command, on the other hand, is a DML operation, which will produce a rollback and thus take longer to complete.
8. Give the reasoning behind using an index.
Faster access to data blocks in a table.
9. Give the two types of tables involved in producing a star schema and the type of data they hold. Fact tables and dimension tables. A fact table contains measurements while dimension tables will contain data that will help describe the fact tables.
10. What type of index should you use on a fact table? A Bitmap index. 11. Give two examples of referential integrity constraints. A primary key and a foreign key. 12. A table is classified as a parent table and you want to drop and re-create it. How would you do this without affecting the children tables? Disable the foreign key constraint to the parent, drop the table, re-create the table, and enable the foreign key constraint.
13. Explain the difference between ARCHIVELOG mode and NOARCHIVELOG mode and the benefits and disadvantages to each. ARCHIVELOG mode is a mode that you can put the database in for creating a backup of all transactions that have occurred in the database so that you can recover to any point in time. NOARCHIVELOG mode is basically the absence of ARCHIVELOG mode and has the disadvantage of not being able to recover to any point in time. NOARCHIVELOG mode does have the advantage of not having to write transactions to an archive log and thus increases the performance of the database slightly.
14. What command would you use to create a backup control file?
ALTER DATABASE BACKUP CONTROLFILE TO TRACE
15. Give the stages of instance startup to a usable state where normal users may access it. STARTUP NOMOUNT - Instance startup
ALTER DATABASE MOUNT - The database is mounted ALTER DATABASE OPEN - The database is opened
16. What column differentiates the V$ views to the GV$ views and how?
The INST_ID column which indicates the instance in a RAC environment the information came from.
17. How would you go about generating an EXPLAIN plan?
Create a plan table with utlxplan.sql.
Use the explain plan set statement_id = 'tst1' into plan_table for a SQL statement
Look at the explain plan with utlxplp.sql or utlxpls.sql
18. How would you go about increasing the buffer cache hit ratio? Use the buffer cache advisory over a given workload and then query the v$db_cache_advice table. If a change was necessary then I would use the alter system set db_cache_size command.
19. Explain an ORA-01555
You get this error when you get a snapshot too old within rollback. It can usually be solved by increasing the undo retention or increasing the size of rollbacks. You should also look at the logic involved in the application getting the error message.
20. Explain the difference between $ORACLE_HOME and $ORACLE_BASE. ORACLE_BASE is the root directory for oracle. ORACLE_HOME located beneath ORACLE_BASE is where the oracle products reside.
21. How would you determine the time zone under which a database was operating? select DBTIMEZONE from dual;
22. Explain the use of setting GLOBAL_NAMES equal to TRUE.
Setting GLOBAL_NAMES dictates how you might connect to a database. This variable is either TRUE or FALSE and if it is set to TRUE it enforces database links to have the same name as the remote database to which they are linking.
23. What command would you use to encrypt a PL/SQL application?
WRAP
24. Explain the difference between a FUNCTION, PROCEDURE and PACKAGE.
A function and procedure are the same in that they are intended to be a collection of PL/SQL code that carries a single task. While a procedure does not have to return any values to the calling application, a function will return a single value. A package on the other hand is a collection of functions and procedures that are grouped together based on their commonality to a business function or application.
25. Explain the use of table functions.
Table functions are designed to return a set of rows through PL/SQL logic but are intended to be used as a normal table or view in a SQL statement. They are also used to pipeline information in an ETL process.
26. Name three advisory statistics you can collect.
Buffer Cache Advice, Segment Level Statistics, & Timed Statistics
27. Where in the Oracle directory tree structure are audit traces placed?
In unix $ORACLE_HOME/rdbms/audit, in Windows the event viewer
28. Explain materialized views and how they are used. Materialized views are objects that are reduced sets of information that have been summarized, grouped, or aggregated from base tables. They are typically used in data warehouse or decision support systems.
29. When a user process fails, what background process cleans up after it?
PMON
30. What background process refreshes materialized views?
The Job Queue Processes.
31. How would you determine what sessions are connected and what resources they are waiting for?
Use of V$SESSION and V$SESSION_WAIT
32. Describe what redo logs are.
Redo logs are logical and physical structures that are designed to hold all the changes made to a database and are intended to aid in the recovery of a database.
33. How would you force a log switch?
ALTER SYSTEM SWITCH LOGFILE;
34. Give two methods you could use to determine what DDL changes have been made.
You could use Logminer or Streams
35. What does coalescing a tablespace do?
Coalescing is only valid for dictionary-managed tablespaces and de-fragments space by combining Neighboring free extents into large single extents.
36. What is the difference between a TEMPORARY tablespace and a PERMANENT tablespace? A temporary tablespace is used for temporary objects such as sort structures while permanent tablespaces are used to store those objects meant to be used as the true objects of the database.
37. Name a tablespace automatically created when you create a database.
The SYSTEM tablespace.
38. When creating a user, what permissions must you grant to allow them to connect to the database?
Grant the CONNECT to the user
39. How do you add a data file to a tablespace?
ALTER TABLESPACE <tablespace_name> ADD DATAFILE <datafile_name> SIZE <size>
40. How do you resize a data file?
ALTER DATABASE DATAFILE <datafile_name> RESIZE <new_size>;
41. What view would you use to look at the size of a data file?
DBA_DATA_FILES
42. What view would you use to determine free space in a tablespace?
DBA_FREE_SPACE
43. How would you determine who has added a row to a table?
Turn on fine grain auditing for the table. 44. How can you rebuild an index? ALTER INDEX <index_name> REBUILD ONLINE;
45. Explain Partitioning and benefits of using Partioning.
Partitioning is a method of taking large tables and indexes and splitting them into smaller, more manageable pieces.
46. You have just compiled a PL/SQL package but got errors, how would you view the errors? SHOW ERRORS 47. How can you gather statistics on a table? The ANALYZE command or DBMS_STAT package. 48. How can you enable a trace for a session? Use the DBMS_SESSION.SET_SQL_TRACE or Use
ALTER SESSION SET SQL_TRACE = TRUE; 49. What is the difference between the SQL*Loader and IMPORT utilities? These two Oracle utilities are used for loading data into the database. The difference is that the import utility relies on the data being produced by another Oracle utility EXPORT while the SQL*Loader utility allows data to be loaded that has been produced by other utilities from different data sources just so long as it conforms to ASCII formatted or delimited files.
50. Name two files used for network connection to a database.
TNSNAMES.ORA and SQLNET.ORA
51. Explain difference between Oracle Database and Instance
Oracle database consist of following: Datafiles, Control Files, Redo Log Files
Oracle instance consist of following: SGA and Oracle processes (DBWR, LGWR, SMON, PMON, ARCH, CKPT, etc.)
52. What is Mutating Table error?
Mutating table error happens when you try to modify the same row you are using it. Use temp table to avoid this error.
53. What is correlated sub-query?
Correlated sub-query is a sub-query, which has reference to the main query
54. Which one of the below change will decrease PAGING/SWAPPING 1. INCREASE SORT_AREA_RETAINED_SIZE 2. DECREASE SHARED_POOL_SIZE (correct answer) 3. DECREASE OPEN_CURSORS parameters 4. INCREASE DB_CACHE_SIZE
55. Explain steps involved in Migration from Oracle 9.0.1 to 9.2.0.6 1. Shutdown 9.0.1 database 2. Apply software patch to new/old ORACLE_HOME 3. Change ORACLE_HOME to point to new 9.2.0.6 binaries 4. STARTUP MIGRATE 5. @ORACLE_HOME/rdbms/admin/catpatch.sql 6. @ORACLE_HOME/rdbms/admin/utlrp.sql 7. Change init.ora parameter COMPATIBLE = 9.2.0.6 8. Shutdown and startup normal
56. Can you create database under any Unix userid besides oracle?
Yes. You can create database user other then oracle as long as that user is part of DBA group in unix
57. Locally Managed TEMP Tablespace is 100% FULL and there is no space available to add datafile to increase TEMP tablespace. What can you do that might free up TEMP space?
You can try one of the following to free up TEMP space 1. Issue ALTTER TABLESPACE PCTINCREASE 1 followed by ALTTER TABLESPACE PCTINCREASE 0 command; 2. Close some of the idle sessions connected to the database
58. List five most important features of Oracle 9i 1. AUTOMATIC UNDO MANAGEMEND 2. AUTOMATICE PGA MEMORY MANAGEMENT 3. MULTI-TABLE INSERT statements 4. EXTERNAL TABLES 5. DYNAMIC MEMORY MANAGEMENT
59. Name five top 9I init.ora parameters affecting performance 1. CURSOR_SHARING 2. DB_CACHE_SIZE 3. PGA_AGGREGATE_TARGET 4. WORKAREA_SIZE_POLICY 5. DB_16K_CACHE_SIZE, DB_8K_CACHE_SIZE, DB_2K_CACHE_SIZE

60. How do you recover database when you lost all of your control files?
In case of loss of loss of all control files, you can still recover database as long as you have all archivelog files. You can issue following command to recover the database. RECOVER DATABASE USING BACKUP CONTROLFILES UNTIL CANCEL; Apply all archivelog files ALTER DATABASE OPEN RESETLOGS; SHUTDOWN IMMEDIATE; Backup database (COLD) STARTUP;
61. What is main purpose of CHECKPOINT?
A Checkpoint is a database event, which synchronizes the data blocks in memory with the datafiles on disk.
A checkpoint has two purposes: 1. to establish data consistency 2. Enable faster database recovery.
62. You got a call from Application team saying Application is running very SLOW. Where do you start looking first? Below are some of very important you should gather to identify the root cause of slowness in application/database. Run a TOP command in unix to see CPU usage (identify CPU killer processes)
Run VMSTAT, SAR, and PRSTAT command to get more information on CPU and memory usage and possible blocking
Run STATSPACK report to identify: a. TOP 5 WAIT EVENTS b. RESOURCE intensive SQL statements
See if STATISTICS on affected tables needs to be re-generated
IF poorly written statements are culprit, run a EXPLAIN PLAN on these statements and see whether new index or use of HINT brings the cost of SQL down.

63. How to SWITCH from PRIMARY to PHYSICAL STANDBY in 9i
Perform below on Primary DB: 1. ALTER DATABASE COMMIT TO SWITCHOVER TO PHYSICAL STANDBY WITH SESSION SHUTDOWN; 2. SHUTDOWN IMMEDIATE; 3. STARTUP NOMOUNT; 4. ALTER DATABASE MOUNT STANDBY DATABASE; 5. RECOVER MANAGED STANDBY DATABASE DICONNECT FROM SESSION; 6. ALTER SYSEM SET LOG_ARCHIVE_DEST_2_STATUS= DEFER SCOPE=SPFILE;
Perform below on STANDBY DB: 7. ALTER DATABASE COMMIT TO SWITCHOVER TO PRIMARY; 8. SHUTDOWN IMMEDIATE; 9. STARTUP; 10. ALTER SYSEM SET LOG_ARCHIVE_DEST_2_STATUS= ENABLE SCOPE=SPFILE;
At this time Standby becomes Primary and Primary becomes new Standby.
64. How to ACTIVATE PHYSICAL STANDBY database in 9i
Perform below on Primary DB if available to transfer all pending archive logs to standby: 1. ALTER SYSTEM SWITCH LOGFILE; 2. ALTER SYSTEM SWITCH LOGFILE;
Perform below on STANDBY DB: 1. ALTER DATABASE ACTIVATE STANDBY DATABASE; 2. SHUTDOWN IMMEDIATE; 3. STARTUP 4. Add TEMP file if needed.
At this time Standby database becomes PRIMARY database and relationship between Primary and
Standby has been lost by activating standby database.
65. Explain different protection mode in DATAGURD MAXIMUM PROTECTION MAXIMUM AVAILIBILITY MAXIMUM PERFORMANCE
66. What is CASCADING STANDBY database?
A CASCADING STANDBY is a standby database that receives its REDO information from another
STANDBY database (not from Primary database).
67. What are some of the dba tables you query to find out about UNDO segments? You would query:
DBA_UNDO_SEGS
V$UNDOSTAT
68. What does Block Media Recovery (BMR) do?
BMR is responsible for restore and recover of specified BLOCK
69. What is the difference between Fine Grained Audit (FGA) and Fine Grained Access Control (FGAC)? FGA tracks when sensitive rows have been accesses, where FGAC prevents access to sensitive rows 70. Which dynamic performance view DBA can query to see who deleted data from a particular table sometime back? V$LOGMNR_CONTENTS 71. What do you use DBMS_REDEFINITION package for? DBMS_REDEFINITION package is used to perform an ONLINE REBUILD of a table 72. How do you add second or subsequent BLOCK SIZE to an existing database?
Re-Create the CONTROLFILE to specify the new BLOCK SIZE for specific data files Or Take the database OFFLINE, and the bring back online with a new BLOCK SIZE specification
73. What are new RMAN features in 9i?
It allows you to set retention period of backups
It enables you to store the CHANNEL attributes so you do not have to specify in each
BACKUP or RESTORE command
74. Explain different PARTITIONING options available in 9i Range Partitioning Used when there are logical ranges of data. Possible usage: dates, part numbers, and serial numbers.
Hash Partitioning Used to spread data evenly over partitions. Possible usage: data has no logical groupings.
List Partitioning Used to list together unrelated data into partitions. Possible usage: a number of states list partitioned into a region.
Composite Range-Hash Partitioning Used to range partition first, then spreads data into hash partitions.
Possible usage: range partition by date of birth then hash partition by name; store the results into the hash partitions.
Composite Range-List Partitioning Used to range partition first, then spreads data into list partitions.
Possible usage: range partition by date of birth then list partition by state, then store the results into the list partitions. 75. How to convert a Single Instance 9i database to a Real Application Clusters 9i (RAC) database without using export/import tools. 1. Make a full database backup before you change anything 2. Copy the existing $ORACLE_HOME/dbs/init<SID1>.ora to $ORACLE_HOME/dbs/init<db_name>.ora. Add the following parameters to $ORACLE_HOME/dbs/init<db_name>.ora: a. *.cluster_database = TRUE b. *.cluster_database_instances = 2 c. *.undo_management=AUTO (Add if you don't have it ) d. <SID1>.undo_tablespace=undotbs (undo tablespace which already exists) e. <SID1>.instance_name=RAC1 f. <SID1>.instance_number=1 g. <SID1>.thread=1 h. <SID1>.local_listener=LISTENER_RAC1 3. Open your database and run $ORACLE_HOME/rdbms/admin/catclust.sql to create cluster database specific views within the existing instance 4. Recreate control file if you defined maxinstances to be 1 when you created the single instance database 5. Add instance specific parameters in the init<db_name>.ora for the second instance on the second node and set appropriate values for it a. <SID2>.instance_name=RAC2 b. <SID2>.instance_number=2 c. <SID2>.local_listener=LISTENER_RAC2 d. <SID2>.thread=2 e. <SID2>.undo_tablespace=UNDOTBS2 f. <SID2>.cluster_database = TRUE g. <SID2>.cluster_database_instances = 2 6. From the first instance, mount the database and run the following command alter database add logfile thread 2 group 3 ('/dev/RAC/redo2_01_100.dbf') size 100M, group 4 ('/dev/RAC/redo2_02_100.dbf') size 100M; alter database enable public thread 2; 7. Create a second Undo Tablespace from the existing instance 8. Set ORACLE_SID and ORACLE_HOME environment variables on the second node and START second instance. 76. Explain RAC and advantages of using RAC In Real Application Clusters environments, all nodes concurrently execute transactions against the same database. Real Application Clusters coordinates each node's access to the shared data to provide consistency and integrity.
Advantages of RAC:
Improved throughput
Scalability over single instance systems
Improved response time
High availability
Transparency
77. Explain Row Locking and Multi-version Read Consistency in RAC Oracle's row locking feature allows multiple transactions from separate nodes to lock and update different rows of the same data block. This is done without any of the transactions waiting for the others to commit. If a row has been modified but not yet committed, then the original row values are available to all instances for read access. This is called multi-version read consistency. 78. What is an External table introduced in 9i? Oracle9i introduces external tables, which provide a mechanism to view data stored in external sources as if it were a table in the database. This ability to read external data provides a more straightforward method of loading and transforming data from external sources. Administrators no longer need to reserve space inside the database for staging tables or write external programs to transform the data outside of the database environment. By making it no longer necessary to stage data in the Oracle database, Oracle9i's external tables have essentially streamlined the ETL function by merging the transformation and loading processes.
79. What is SPFILE?
The SPFILE (server parameter file) is Oracle's new method of maintaining database parameters. The old method of editing a text based parameter file (INIT.ORA) has given way to the new method of maintaining persistent parameters. By this Oracle means that you can change a system parameter and have its value be maintained across shutdown and startup. This is a great savings from the past where you had to issue the ALTER SYSTEM command and then remember to edit the INIT.ORA parameter file. Here is how to create SPFILE: SQL> CREATE SPFILE [='spfile_name'] FROM PFILE [='pfile_name']; SQL> CREATE PFILE [='pfile_name'] FROM SPFILE [='spfile_name']; SQL> create spfile from pfile;
Usage:
1. SQL> ALTER SYSTEM SET DB_CACHE_SIZE=1000M SCOPE=SPFILE;
80. How do you backup and restore using Transportable Tablespaces
1.Run DBMS_TTS against the tablespace to see if tablespace is self contained or not.
2. Make tablespace Read Only.
3. Export Metadata (EXP TRANSPORT_TABLESPACES=Y TABLESPACE=ts1)
4. Copy data file to target host
5. Copy export dump to target
6. Import the Metadata (IMP TRANSPORT_TABLESPACES=Y DATAFILES (file1,file2) )
7. Bring Tablespace ONLINE and enable SOURCE tablespace to READ WRITE

81. Explain different type of Database Failures
Statement failure failed SQL is automatically rolled back and an error is returned to user.
User Process failure abnormal disconnect PMON detects and rolls back and releases locks.
User Error (drop table, data) DBA is required to recover data (import or incomplete recovery)
Media Failure Loss or corruption of files DBA needs to apply appropriate recovery.
Instance Failure Abnormal shutdown Instance simply needs restarted, SMON auto recovers by:
Rolling forward changes in the redo log not recorded in the data files before Open of database. Rollbacks can occur after the database is open, when block data is requested.

82. What does RESETLOGS option do?
1. Creates a new incarnation of the database, putting a new SCN in all data file headers.
2. Reset Log Sequence number to 1
3. Reformats ONLINE REDO LOGFILES if they exists
83. Name 5 system views that can be used to retrieve information about backup and recovery
V$BACKUP
V$DATAFILE_HEADER
V$RECOVER_FILE
V$RECOVERY_LOG
V$RECOVERY_STATUS
84. What is the quickest way to clone a database give your backup is done via RMAN?
Using RMAN command DUPLICATE DATABASE
85. What is the use of the RESUMABLE parameter in EXPORT?
The RESUMABLE parameter allows the export to 1. Suspend if a space allocation issue occurs 2. Wait until the space allocation issue is solved 3. Then resume and therefore not to abort, provided a timeout is set appropriately.
86. Name init.ora parameters need to set for Advanced Replication
DISTRIBUTED_TRANSACTIONS
GLOBAL_NAMES
JOB_QUEUE_PROCESSES
OPEN_LINKS
PARALLEL_MAX_SERVERS
PARALLEL_MIN_SERVERS
87. Name 5 init.ora parameters that needs to set in Primary database for DataGuard configuration
LOG_ARCHIVE_DEST_2
LOG_ARCHIVE_DEST_2_STATE
FAL_CLIENT
FAL_SERVER
STANDBY_ARCHIVE_DEST
STANDBY_FILE_MANAGEMENT
88. What is the use of FORCE LOGGING option? By setting FORCE LOGGING to TRUE, all transactions will generate REDO. This is used for Data Guard, so no data will be missed (i.e. transactions that were run with NOLOGGING option) in Standby database.
89. (On UNIX) When should more than one DB writer process be used? How many should be used?
If the UNIX system being used is capable of asynchronous IO then only one is required, if the system is not capable of asynchronous IO then up to twice the number of disks used by Oracle number of DB writers should be specified by use of the db_writers initialization parameter.
90. If you have an example table, what is the best way to get sizing data for the production table implementation? The best way is to analyze the table and then use the data provided in the DBA_TABLES view to get the average row length and other pertinent data for the calculation. The quick and dirty way is to look at the number of blocks the table is actually using and ratio the number of rows in the table to its number of blocks against the number of expected rows.
91. What special Oracle feature allows you to specify how the cost based system treats a SQL statement? The COST based system allows the use of Hints to control the optimizer path selection. If they can give some example hints such as FIRST ROWS, ALL ROWS, USING INDEX, STAR, even better.
92. You want to determine the location of identical rows in a table before attempting to place a unique index on the table, how can this be done? select rowid from emp e where e.rowid > (select min(x.rowid) from emp x where x.emp_no = e.emp_no); 93. You are joining a local and a remote table, the network manager complains about the traffic involved, how can you reduce the network traffic?
Push the processing of the remote data to the remote instance by using a view to pre-select the information for the join. This will result in only the data required for the join being sent across.
94. How do you prevent output from coming to the screen?
The SET option TERMOUT controls output to the screen. Setting TERMOUT OFF turns off screen output. This option can be shortened to TERM.
95. You see multiple fragments in the SYSTEM tablespace, what should you check first?
Ensure that users don¡¯t have the SYSTEM tablespace as their TEMPORARY or DEFAULT tablespace assignment by checking the DBA_USERS view.
96. What are some indications that you need to increase the SHARED_POOL_SIZE parameter? Poor data dictionary or library cache hit ratios, getting error ORA-04031. Another indication is steadily decreasing performance with all other tuning parameters the same.
97. When should you increase copy latches? What parameters control copy latches?
When you get excessive contention for the copy latches as shown by the ¡°redo copy latch hit ratio. You can increase copy latches via the initialization parameter LOG_SIMULTANEOUS_COPIES to twice the number of CPUs on your system.
98. Describe hit ratio as it pertains to the database buffers. What is the difference between instantaneous and cumulative hit ratio and which should be used for tuning? The hit ratio is a measure of how many times the database was able to read a value from the buffers verses how many times it had to re-read a data value from the disks. A value greater than 80-90% is good, less could indicate problems. If you simply take the ratio of existing parameters this will be a cumulative value since the database started. If you do a comparison between pairs of readings based on some arbitrary time span, this is the instantaneous ratio for that time span. Generally speaking an instantaneous reading gives more valuable data since it will tell you what your instance is doing for the time it was generated over.
99. What can cause a high value for recursive calls? How can this be fixed?
A high value for recursive calls is cause by improper cursor usage, excessive dynamic space management actions, and or excessive statement re-parses. You need to determine the cause and correct it By either re-linking applications to hold cursors, use proper space management techniques (proper storage and sizing) or ensure repeat queries are placed in packages for proper reuse.
100. You look at the dba_rollback_segs view and see that there is a large number of shrinks and they are of relatively small size, is this a problem? How can it be fixed if it is a problem? A large number of small shrinks indicates a need to increase the size of the rollback segment extents. Ideally you should have no shrinks or a small number of large shrinks. To fix this just increase the size of the extents and adjust optimal accordingly. 101. You look at the dba_rollback_segs view and see that you have a large number of wraps is this a problem? A large number of wraps indicates that your extent size for your rollback segments are probably too small. Increase the size of your extents to reduce the number of wraps. You can look at the average transaction size in the same view to get the information on transaction size.
102. How many redo logs should you have and how should they be configured for maximum recoverability? You should have at least three groups of two redo logs with the two logs each on a separate disk spindle (mirrored by Oracle). The redo logs should not be on raw devices on UNIX if it can be avoided.
103. If the database cannot be bounced, how would you kill a user?
Use command: ALTER SYSTEM KILL SESSION SID,SERIAL# ;
104: What is the frequency of log Updated..?
On commit or
On checkpoint or
Redolog buffer is 1/3rd full
105: How do you rename a database?
You can change Database name by following below procedure:
1. Alter Database backup control file to trace;
2. Above step will create a text control file in user_dump_dest directory.
3. Change name of the Database in above file and in init.ora file.
4. STARTUP NOMOUNT
5. Run the script that was modified in step 3
6. ALTER DATABASE OPEN RESETLOGS;

106: Is it possible to configure primary server and stand by server on different OS? Answer for this questions is NO. Standby database must be on same version of database and same version of Operating system.
107: What does database do during mounting process?
While mounting the database oracle reads the data from controlfile which is used for verifying physical database files during sanity check. Background processes are started before mounting the database only.
108: What is a deadlock and Explain
A deadlock is a condition where two or more users are waiting for data locked by each other. Oracle automatically detects a deadlock and resolves them by rolling back one of the statements involved in the deadlock, thus releasing one set of data locked by that statement. Statement rolled back is usually the one which detects the deadlock. Deadlocks are mostly caused by explicit locking because oracle does not do lock escalation and does not use read locks. Multi-table deadlocks can be avoided by locking the tables in same order in all the applications, thus precluding a deadlock.
109: What are the options available to refresh snapshots?
COMPLETE - Tables are completely regenerated using the snapshots query and the master tables every time the snapshot referenced.
FAST - If simple snapshot used then a snapshot log can be used to send the changes to the snapshot tables.
FORCE - Default value. If possible it performs a FAST refresh; otherwise it will perform a complete refresh.
110: What is snapshot log? It is a table that maintains a record of modifications to the master table in a snapshot. It is stored in the same database as master table and is only available for simple snapshots. It should be created before creating snapshots.
111: What is Two-Phase Commit?
Two-phase commit is mechanism that guarantees a distributed transaction either commits on all involved nodes or rolls back on all involved nodes to maintain data consistency across the global distributed database. It has two phase, a Prepare Phase and a Commit Phase.
112: Describe two phases of Two-phase commit?
Prepare phase - The global coordinator (initiating node) ask a participants to prepare (to promise to commit or rollback the transaction, even if there is a failure)
Commit - Phase - If all participants respond to the coordinator that they are prepared, the coordinator asks all nodes to commit the transaction, if all participants cannot prepare, the coordinator asks all nodes to roll back the transaction.
113: What are the factors causing the reparsing of SQL statements in SGA
There are main two causes for reparsing:
1. The objects which the query is referencing has been modified
2. The parsed version of sql text has been aged out of the library cache.
114: How to implement the multiple control files for an existing database 1. Edit init.ora file, set control_files parameter with multiple location
2. shutdown immediate
3. copy control file to multiple locations & confirm from init.ora contol_files parameter
4. start the database.
5. run this query for changes confirmation - select name from v$controlfile;
115: What is mean by Program Global Area (PGA)
PGA - Program Global Area or the Process Global Area is a memory region that contains data and control information for a single server process or a single background process.
The PGA is allocated when a process is created and de-allocated when the process is terminated. PGA is an area that is used by only one process.
116: What is meant by recursive hints?
Number of times processes repeatedly query the dictionary table is called recursive hints. It is due to the data dictionary cache is too small. By increasing the SHARED_POOL_SIZE parameter we can optimize the size of Data Dictionary Cache.
117: Is it possible to use raw devices as data files and what is the advantages over filesystem files ? Yes.
The advantages over file system files:
I/O will be improved because Oracle will bypass the OS. Disk Corruption will be very less.
118: What are disadvantages of having raw devices?
We have to depend on export/import utility for backup/recovery The tar command cannot be used for physical file backup, instead we have to use dd command which is less flexible and has limited recoveries.
119. What are the system resources that can be controlled by profile?
1. Number of concurrent sessions by user
2. CPU processing time
3. Amount of Logical I/O
4. Amount of Idle time
120. Explain different level of Auditing
Statement Auditing
Privilege Auditing
Object Auditing
121. Explain the difference between $ORACLE_HOME and $ORACLE_BASE. ORACLE_BASE is the root directory for oracle. ORACLE_HOME located beneath ORACLE_BASE is where the oracle products reside.
122. Name three advisory statistics you can collect.
Database Cache Advisory
Shared Pool Advisory
PGA Advisory
123. When a user process fails, what background process cleans up after it?
PMON
124. How would you force a log switch?
ALTER SYSTEM SWITCH LOGFILE;
125. When creating a user, what permissions must you grant to allow them to connect to the database? CREATE SESSION
126. What view would you use to determine free space in a tablespace?
DBA_FREE_SPACE
127. How would you determine who has added a row to a table?
If database auditing is turned ON, query SYS.AUD$ table
128. You have just compiled a PL/SQL package but got errors, how would you view the errors? SHOW ERRORS
129. How can you enable a trace for a session?
ALTER SESSION SET TRACING ON
130. A DBA had to remove some Archivelogs to free up space in filesystem.
Now when the RMAN job starts to backup Archivelogs, it complains about missing Archivelogs that were deleted by DBA. To resolve the issue and continue backing up remainder of Archivelogs, which RMAN command can be used so it won't complain about missing Archivelogs. Crosscheck command 131. Which RMAN command is used to create an exact replica of a database in new host? DUPLICATE DATABASE 132. How do you install STATSPACK? By running $ORACLE_HOME/rdbms/admin/spcreate.sql script
133. Process you follow to start looking into Performance issue at database level (If the application is running very slow, at what points do you need to go about the database in order to improve the performance?) Run a TOP command in Unix to see CPU usage (identify CPU killer processes)
Run VMSTAT, SAR, and PRSTAT command to get more information on CPU and memory usage and possible blocking
Run STATSPACK report to identify: 1. TOP 5 WAIT EVENTS 2. RESOURCE intensive SQL statements
See if STATISTICS on affected tables needs to be re-generated
IF poorly written statements are culprit, run a EXPLAIN PLAN on these statements and see whether new index or use of HINT brings the cost of SQL down.
134. Which is most important v$ view to see performance related information?
V$WAITSTAT
135. Explain below wait events in STATSPACK report
DB SCATTERED READ, DB SEQUENTIAL REAL, ENQUEUE
DB SCATTERED READ, Full tables scan
DB SEQUENTIAL REAL, IO
ENQUEUE Locking
135. List five most important parameter in 9i affecting performance
CURSOR_SHARING
DB_CACHE_SIZE
PGA_AGGREGATE_TARGET
DB_16K_CACHE_SIZE, DB_8K_CACHE_SIZE, DB_2K_CACHE_SIZE
136. What is PGA_AGGREGATE_TARGET?
This parameter controls the maximum amount of memory PGA which can be used by the queries when WORKAREA_SIZE_POLICY is set to Auto. The value you can be set in Bytes, kilobytes (K), megabytes (M) or gigabytes (G). The default value is 0 This parameter also has an effect on the execution plans of the cost based optimizer. The optimizer usesthe value of the parameter PGA_AGGREGATE_TARGET to derive an estimate for the minimum andmaximum amount of memory which should be available at run-time for each sort, hash-join and bitmapoperator in the query. Based on this minimum and maximum value, the optimizer selects the best plan.
137. How do you analyze table partition using Oracle provided package?
DBMS_STATS.GATHER_TABLE_STATS with GRANULARITY => 'PARTITION' OPTION
138. You see a wait on LMS process in statspack, what does that mean?
A. Wait is due to Data Guard Broker.
139. Name three advisory statistics you can collect.
SHARED_POOL_ADVICE
PGA_TARGET_ADVICE
DB_CACHE_ADVICE
140. Explain procedure to Change CHARACTERSET of a database.
Can't change CHARACTERSET of a database, you will need to re-create the database with appropriate CHARACTERSET.
141. If you had a tablespace, TEST_TABLESPACE, which consists of three files:
TEST01.dbf, TEST02.dbf, and TEST03.dbf, and someone accidentally used the Unix command "rm" to delete the file TEST02.dbf, what else would you need in order to recover all the data that was present in TEST_TABLESPACE at the time that TEST02.dbf was deleted?
All Archivelogs
142. How do you put database is ARCHIVELOG mode, explain procedure
1. Modify init.ora parameter START_ARCHIVE=TRUE
2. SQL> SHUTDOWN IMMEDIATE;
3. STARTUP MOUNT;
4. ALTER DATAVASE ARCHIVELOG;
5. ALTER DATABASE OPEN;
143. How do you create PASSWORD FILE? using orapwd utility
144. How can you tell if an index on particular table is USED or NOT USED in 9i?
By turning MONITORING ON that index and querying into INDEX_USAGE table
145. How do you switch from an init.ora file to a spfile?
SQL> CREATE SPFILE FROM PFILE;
146. Explain FORCE LOGGING feature in 9i.
By setting FORCE LOGGING to TRUE, all transactions will generate REDO. This is used for Data Guard, so no data will be missed (i.e. transactions that were run with NOLOGGING option) in Standby database
147. Explain the use of setting GLOBAL_NAMES equal to TRUE.
Setting GLOBAL_NAMES dictates how you might connect to a database. This variable is either TRUE or FALSE and if it is set to TRUE it enforces database links to have the same name as the remote database to which they are linking.
148. How do you set up 9i Data Guard?
Take a full hot backup of Primary database
Create standby control file
Transfer full backup, init.ora, standby control file to standby node.
Modify init.ora file on standby node.
Restore database
Recover Standby database (Alternatively, RMAN command DUPLICATE DATABASE FOR STANDBY DO RECOVERY can be also used)
Setup FAL_CLIENT and FAL_SERVER parameters on both sides
Put Standby database in Managed Recover mode
149. How do you create Physical Standby database?
Take a full hot backup of Primary database
Create standby control file
Transfer full backup, init.ora, standby control file to standby node.
Modify init.ora file on standby node.
Restore database
Recover Standby database (Alternatively, RMAN command DUPLICATE DATABASE FOR STANDBY DO RECOVERY can be also used)
Setup FAL_CLIENT and FAL_SERVER parameters on both sides
Put Standby database in Managed Recover mode
150. Explain LOG_ARCHIVE_DEST_2 parameter and Dataguard related parameters. log_archive_dest_2='SERVICE=ORACLE_SID_STBY optional lgwr async=20480 noaffirm reopen=15 max_failure=10 net_timeout=30 delay=0' 151. Explain Database SWITCH OVER PROCEDURE On Primary: alter database commit to switchover to physical standby with session shutdown; shutdown; startup nomount; alter database mount standby database; recover managed standby database disconnect from session;
On Standby: alter database commit to switchover to primary; shutdown; startup;
152. Exaplain How to Activate STANDBY Database
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;
ALTER DATABASE ACTIVATE STANDBY DATABASE;
SHUTDOWN IMMEDIATE;
STARTUP;
153. What do you know about VCS?
VCS stands for Veritas Cluster Software. VCS is used as a High Availability solution in case of host failure. There will be typically two nodes in a cluster and database will be running on one node. Incase of host failure, VCS will failover database (service group) to second node.
154. What are typical resources in VCS service group?
In typical VCS configuration, there are three main resources required for Oracle database failover.
1. Oracle Database
2. Listener
3. Filesystems
155. Which file contains VCS service group and resource information?
Main.cf
156. What database related information we need to set in VCS?
ORACLE_SID
LISTENER name
LISTENER password (if used)
Oracle filesystems that will be failed over
Location to init.ora/spfile if not available at default location
157. What is VCS in-depth monitoring?
In VCS in-depth monitoring, a database user (VCSMON) will be created which will login to database at certain interval (i.e. every 5 minute) to see if database connectivity is OK. For some reason, if this user can t login VCS will fail over the database to second node.
158. In ACTIVE VCS environment, you need to recycle the database but doesn’t want database to failover to other node. What you must do before shutting down the database, so it doesn t failover to other node? You need to FREEZE the service group.
Alternatively, you can make Oracle resource NON-CRITICAL (not recommended)
159. What if you accidentally shutdown the LISTENER in VCS environment?
If Listener Resource is marked CRITICAL, and Restart Attempt is set to 0, then Service Group will failover to second node.
It is recommended for Listener resource to set RESTART ATTEMPTS value to 3.
160. Explain Automatic Segment Space Management
Automatic Segment Space Management features was introduced in 9i which simplifies management of free space usage within object for below parameter:
FREELIST
FREELIST GROUPS
PCTUSED
161. How do you REBUILD index online and Compute Statistics at the same time?
ALTER INDEX INDEX_NAME REBUILD COMPUTE STATISTICS ONLINE;
162. Explain Bitmap Join Indexes
Bitmap Join Indexes pre-stores results of a join and can avoid an expensive join operation at runtime.
162. Which parameters can be modified dynamically as part of 9i Dynamic Memory Management feature? Below parameters can be modified dynamically as part of 9i Dynamic Memory Management feature
DB_CACHE_SIZE
SHARED_POOL_SIZE
LARGE_POOL_SIZE
JAVA_POOL_SIZE
163. What additional statistics are gathered by DBMS_STATS that were not available in earlier version or by using ANALYE command? In 9i DBMS_STATS package now collects below statistics as well:
CPU Usage
System I/O
163. Explain Different values supported by CURSOR_SHARING parameter and its explanation Below values are supported by CURSOR_SHARING init.ora parameter:
FORCE - Literals will be replaced by system generated bind variables where possible
SIMILAR - Oracle determines which literals are "safe" for substitution with bind variables. This will result in some SQL not being shared in an attempt to provide a more efficient execution plan.
EXACT - Only allows statements with identical text to share the same cursor
163. Name three very important Hit Ratios in database Buffer Cache Hit Ratio (Use V$SYSSTAT)
Data Dictionary Hit Ratio (Use V$ROWCACHE)
Library Cache Hit Ratio (Use V$LIBRARYCACHE, V$SGASTAT)
164. Name Different Latches in database and Dynamic Performance Views to get more information about Latches Database Latches:
Redo Allocation Latch
Redo Copy Latch
Row Cache Latch
Use V$LATCH, V$LATCHHOLDER, V$LATCHNAME to get more information about the latches
165. In which scenarios you need to set Large Pool?
You need to set Large Pool if you are using below:
MTS (Multithreaded Server)
RMAN backups
166. Explain Tuning Process that involves Application, Database, OS, Network
In such a scenario, tuning should perform in following order: 1. Business Rules 2. Data Design 3. Application Design 4. Logical Structure of the Database 5. Database Operations 6. Access Path 7. Memory Allocation 8. I/O and Physical Structure of the Database 9. Resource Allocation 10. OS
167. Explain Different Tuning Areas in Database
Following areas within database can be tuned:
Memory Shared Pool, Buffer Cache, Redo Buffer, Sort Area Size, PGA, Large Pool
I/O Multiple Database Writer Processes, Distributing I/O, RAID
CPU
Space Management Extent Allocation, Oracle Block Efficiency
Redo & Checkpoint Redo log file configuration, checkpoints
Rollback Retention, number of Rollback Segments, Optimal
168. How do you setup Auditing in Database?
If audit packages are not installed, run $ORACLE_HOME/rdbms/admin/cataudit.sql script
Modify initialization parameter AUDIT_TRAIL=DB and setup AUDIT_DUMP_DEST
Select what type of operations needs to be audited
View Audit results from SYS.AUD$ table
169. Can you Audit System Operations? If Yes, how?
SYS connections can be audited by setting init.ora parameter AUDIT_SYS_OPERATIONS=TRUE
170. How can you setup Encryption in Database?
Data within Database can be encrypted and decrypted using package:
DBMS_OBFUSCATION_TOOLKIT
171. Name five parameters can be used for Password Management?
Following parameters can be used to manage user password:
FAILED_LOGIN_ATTEMPTS
PASSWORD_GRACE_TIME
PASSWORD_LIFE_TIME
PASSWORD_REUSE_MAX
PASSWORD_REUSE_TIME
172: What is difference between Logical Standby Database and Physical Standby database? The primary functional difference between logical and physical standby database setups is that logical standby permits you to add additional objects (tables, indexes, etc) to the database, while physical standby is always an exact structural duplicate of the master database. The downside, though, is that logical standby is based on newer technologies (logical standby is new in Oracle 9.2) and tends to be generally regarded as more temperamental than physical standby.

MID LEVEL ORACLE DBA INTERVIEW QUESTIONS

1: What is difference between Co-related sub query and nested sub query? Co-related sub query is one in which inner query is evaluated only once and from that result outer query is evaluated. Nested query is one in which Inner query is evaluated for multiple times for getting one row of that outer query. ex. Query used with IN() clause is Co-related query.
Query used with = operator is Nested query 2: How do I write a cron which will run a SQL query and mail the results to a group? Use DBMS_JOB for scheduling a cron job and DBMS_MAIL to send the results throught email. 3: What operator performs pattern matching
LIKE operator 4: What is the use of the DROP option in the ALTER TABLE command
It is used to drop constraints specified on the table. 5: Which date function is used to find the difference between two dates
MONTHS_BETWEEN
6: What is the advantage of specifying WITH GRANT OPTION in the GRANT command?
The privilege receiver can further grant the privileges he/she has obtained from the owner to any other user. 7: What is the use of CASCADE CONSTRAINTS
When this clause is used with the DROP command, a parent table can be dropped even when a child table exists. 8: Which function is used to find the largest integer less than or equal to a specific value FLOOR 9: What operator tests column for the absence of data
IS NULL operator 10: What are the steps involved in Database Startup?
Start an instance, Mount the Database and Open the Database. 11: What are the steps involved in Database Shutdown?
Close the Database; Dismount the Database and Shutdown the Instance. 12: What is Restricted Mode of Instance Startup?
An instance can be started in (or later altered to be in) restricted mode so that when the database is open connections are limited only to those whose user accounts have been granted the RESTRICTED SESSION system privilege. 13: What are the different modes of mounting a Database with the Parallel Server?
Exclusive Mode If the first instance that mounts a database does so in exclusive mode, only that Instance can mount the database.
Parallel Mode If the first instance that mounts a database is started in parallel mode, other instances that are started in parallel mode can also mount the database. 14: What is Full Backup?
A full backup is an operating system backup of all data files, on-line redo log files and control file that constitute ORACLE database and the parameter. 15: Can Full Backup be performed when the database is open? No. 16: What is Partial Backup? A Partial Backup is any operating system backup short of a full backup, taken while the database is open or shut down. 17: What is On-line Redo Log? The On-line Redo Log is a set of tow or more on-line redo files that record all committed changes made to the database. Whenever a transaction is committed, the corresponding redo entries temporarily stores in redo log buffers of the SGA are written to an on-line redo log file by the background process LGWR. The on-line redo log files are used in cyclical fashion. 18: What is Mirrored on-line Redo Log? A mirrored on-line redo log consists of copies of on-line redo log files physically located on separate disks; changes made to one member of the group are made to all members. 19: What is Archived Redo Log? Archived Redo Log consists of Redo Log files that have archived before being reused. 20: What are the advantages of operating a database in ARCHIVELOG mode over operating it in NO ARCHIVELOG mode? Complete database recovery from disk failure is possible only in ARCHIVELOG mode. Online database backup is possible only in ARCHIVELOG mode. 21: What is Log Switch?
The point at which ORACLE ends writing to one online redo log file and begins writing to another is called a log switch. 22: What are the steps involved in Instance Recovery?
Rolling forward to recover data that has not been recorded in data files, yet has been recorded in the on-line redo log, including the contents of rollback segments. Rolling back transactions that have been explicitly rolled back or have not been committed as indicated by the rollback segments regenerated in step a.
Releasing any resources (locks) held by transactions in process at the time of the failure.
Resolving any pending distributed transactions undergoing a two-phase commit at the time of the instance failure. 23: Do you need a commit after DDL statements?
DDL IS A AUTO COMMIT YOU DON T NEED TO COMMIT AGAIN 24: How would you pass hints to the SQL processor?
USING COMMENT LINES WITH (+) SIGN YOU CAN PASS THE HINTS TO SQL ENGINE
For example /* +PARALLEL( ) */ 25: what is the difference between group by and order by?
Group by is used when we use aggregate functions on the columns in a query the other columns should be in group by query eg: select empno,ename,sum(sal) from emp group by empno,ename
Order by is used to sort values either in ascending or descending order 26: What are the Large object types supported by Oracle?
BLOB
CLOB
NLOB
These usually support data up to 4GB 27: What are the Characteristics of Data Files?
A data file can be associated with only one database. Once created a data file can't change size. One or more data files form a logical unit of database storage called a tablespace 28: What is the difference between SID and Global Database Name? SID (System Identifier) : A SID (almost) uniquely identifies an instance. Actually, $ORACLE_HOME, $ORACLE_SID and $HOSTNAME identify an instance uniquely. The SID is 64 characters, or less; at least on Oracle 9i. The system identifier is included in the CONNECT_DATA parts of the connect descriptors in a tnsnames.ora file. The SID defaults to the database name.
Global Database Name : A database is uniquely identified by a global database name. Usually, a global database name has the form somename.domain. The global database name is the composit of db_domain and db_name. 29: What is the difference between materialized view and snapshot?
A materialized view is a replica of a target master from a single point in time. The concept was first introduced with Oracle7 termed as SNAPSHOT. In Oracle release 7.1.6 snapshots were enhanced to enable DMLs along with a new terminology, updatable snapshots. With Oracle8.1.6 snapshots started to be used in data warehouse environments so anew terminology materialized view was introduced to address both distributed and data warehouse materialized views. 30: What are the components of Physical database structure of Oracle Database?
ORACLE database is comprised of three types of files. One or more Data files, two are more Redo Log files, and one or more Control files. 31: What is a Temporary Segment?
Temporary segments are created by ORACLE when a SQL statement needs a temporary work area to complete execution. When the statement finishes execution, the temporary segment extents are released to the system for future use. 32: What is a Data File? Every ORACLE database has one or more physical data files. A database's data files contain all the database data. The data of logical database structures such as tables and indexes is physically stored in the data files allocated for a database. 33: What is a Redo Log? The set of Redo Log files for a database is collectively known as the database's redo log. 34: What is the function of Redo Log? The Primary function of the redo log is to record all changes made to data. 35: What is the use of Redo Log Information? The Information in a redo log file is used only to recover the database from a system or media failure prevents database data from being written to a database's data files. 36: What does a Control file Contain? A Control file records the physical structure of the database. It contains the following information. Database Name Names and locations of a database's files and redo log files. Time stamp of database creation. 37: What is the use of Control File? When an instance of an ORACLE database is started, its control file is used to identify the database and redo log files that must be opened for database operation to proceed. It is also used in database recovery. 38: What is a Data Dictionary? The data dictionary of an ORACLE database is a set of tables and views that are used as a read- only reference about the database. It stores information about both the logical and physical structure of the database, the valid users of an ORACLE database, integrity constraints defined for tables in the database and space allocated for a schema object and how much of it is being used. 39: What is an Integrity Constrains?
An integrity constraint is a declarative way to define a business rule for a column of a table. 40: Describe the different type of Integrity Constraints supported by ORACLE?
NOT NULL Constraint - Disallows Nulls in a table's column.
UNIQUE Constraint - Disallows duplicate values in a column or set of columns.
PRIMARY KEY Constraint - Disallows duplicate values and Nulls in a column or set of columns.
FOREIGN KEY Constrain - Require each value in a column or set of columns match a value in a related table's UNIQUE or PRIMARY KEY.
CHECK Constraint - Disallows values that do not satisfy the logical expression of the constraint. 41: What is difference between UNIQUE constraint and PRIMARY KEY constraint? A column defined as UNIQUE can contain Nulls while a column defined as PRIMARY KEY can't contain Nulls. 42: Describe Referential Integrity? A rule defined on a column (or set of columns) in one table that allows the insert or update of a row only if the value for the column or set of columns (the dependent value) matches a value in a column of a related table (the referenced value). It also specifies the type of data manipulation allowed on referenced data and the action to be performed on dependent data as a result of any action on referenced data.
43: What are the Referential actions supported by FOREIGN KEY integrity constraint? UPDATE and DELETE Restrict - A referential integrity rule that disallows the update or deletion of referenced data.
DELETE Cascade - When a referenced row is deleted all associated dependent rows are deleted 44: What is a Tablespace?
A database is divided into Logical Storage Unit called tablespace. A tablespace is used to grouped related logical structures together. 45: What is SYSTEM tablespace and when is it Created?
Every ORACLE database contains a tablespace named SYSTEM, which is automatically created when the database is created. The SYSTEM tablespace always contains the data dictionary tables for the entire database. 46: Explain the relationship among Database, Tablespace and Data file.
Each databases logically divided into one or more tablespaces. One or more data files are explicitly created for each tablespace. 47: What are synonyms used for?
Synonyms are used to:
Mask the real name and owner of an object.
Provide public access to an object
Provide location transparency for tables, views or program units of a remote database.
Simplify the SQL statements for database users. 48: What are Clusters?
Clusters are groups of one or more tables physically stores together to share common columns and are often used together. 49: When can Hash Cluster used?
Hash clusters are better choice when a table is often queried with equality queries. For such queries the specified cluster key value is hashed. The resulting hash key value points directly to the area on disk that stores the specified rows. 50: What is Row Chaining? In Circumstances, all of the data for a row in a table may not be able to fit in the same data block. When this occurs, the data for the row is stored in a chain of data block (one or more) reserved for that segment. 51: What is Data Concurrency and Consistency?
Data Concurrency => Means that many users can access data at the same time.
Data Consistency => Means that each user sees a consistent view of the data, including visible changes made by the user's own transactions and transactions of other users. 52: What is Overloading of procedures?
The Same procedure name is repeated with parameters of different datatypes and parameters in different positions, varying number of parameters is called overloading of procedures. e.g. DBMS_OUTPUT.put_line 53: What are % TYPE and % ROWTYPE ? What are the advantages of using these over datatypes?
% TYPE provides the data type of a variable or a database column to that variable.
% ROWTYPE provides the record type that represents a entire row of a table or view or columns selected in the cursor.
The advantages are: You don t need to know about variable's data type ii. If the database definition of a column in a table changes, the data type of a variable changes accordingly. 54: Explain the two type of Cursors?
There are two types of cursors, Implicit Cursor and Explicit Cursor.
PL/SQL uses Implicit Cursors for queries.
User defined cursors are called Explicit Cursors. They can be declared and used. 55: What are the PL/SQL Statements used in cursor processing?
DECLARE CURSOR cursor name, OPEN cursor name, FETCH cursor name INTO or Record types, CLOSE cursor name 56: What is a database trigger? Name some usages of database trigger? Database trigger is stored PL/SQL program unit associated with a specific database table.
Usages are Audit data modifications, Log events transparently, Enforce complex business rules Derive column values automatically, Implement complex security authorizations. Maintain replicate tables. 57: What are the return values of functions SQLCODE and SQLERRM? SQLCODE returns the latest code of the error that has occurred.
SQLERRM returns the relevant error message of the SQLCODE. 58: Explain UNION, MINUS, UNION ALL and INTERSECT UNION - the values of the first query are returned with the values of the second query eliminating duplicates.
MINUS - the values of the first query are returned with duplicates values of the second query removed from the first query.
UNION ALL - the values of both queries are returned including all duplicates 59: How do I eliminate the duplicate rows? Delete from emp a where a.rowid > ( select min(rowid) from emp b where a.empno = b.empno group by empno) 60: Explain CONNECT BY PRIOR TO
The start with .. connect by clause can be used to select data that has a hierarchical relationship (usually some sort of parent->child (boss->employee or thing->parts). 61: What is correlated sub-query?
A correlated sub-query is a subquery that references the value/s from the main query.
62: What is the use of SAVEPOINTS?
SAVEPOINTS are used to subdivide a transaction into smaller parts. It enables rolling back part of a transaction. Maximum of five save points are allowed 63: What is normalization? What is the advantage of normalization (briefly) Database normalization is a series of steps followed to obtain a database design that allows for consistent storage and efficient access of data in a relational database .These steps reduce data redundancy and the risk of data becoming inconsistent 64: What are the components of physical database structure of Oracle database ORACLE database is comprised of three types of files. One or more Data files, two or more Redo Log files, and one or more Control files. 65: What are different types of segments? temp segment, undo segment, table segment, index segment 66: Can you name few DBMS packages and their use?
DBMS_OUTPUT.PUT_LINE('strings');
print out the strings
DBMS_UTILITY.get_time()
get the current time
DBMS_JOBS
to schedule jobs in database
DBMS_STATS
To gather database statistics
67: How can you determine the size of the database?
You can query dba_data_files and dba_temp_files
68: How do you find whether the instance was started with pfile or spfile
There are 3 different ways :-
1) SELECT name, value FROM v$parameter WHERE name = 'SPFILE'; //This query will return NULL if you are using PFILE
2) SHOW PARAMETER spfile // This query will returns NULL in the value column if you are using pfile and not spfile
3) SELECT COUNT(*) FROM v$spparameter WHERE value IS NOT NULL; // if the count is non- zero then the instance is using a spfile, and if the count is zero then it is using a pfile:
By Default oracle will look into the default location depends on the o/s. Like in unix, oracle will check in $oracle_home/dbs directory and on windows it will check in oracle_home/database directory, and the content of pfile is just text based, but spfile content is in binary format, that is understandable by oracle very well.
Also oracle server always checks the spfile or pfile with these sequences:-
SPFILE<SID>.ORA
SPFILE.ORA
PFILE<SID>.ORA
PFILE.ORA 69: How do you pin an object. Use dbms_shared_pool procedure.
EXECUTE DBMS_SHARED_POOL.KEEP(OBJECTNAME); 70: What is the use of COMPRESS option in EXP command? Flag to indicate whether export should compress fragmented segments into single extents. 71: How can you find out within a PL/SQL block if a CURSOR is open or not By using %ISOPEN cursor status variable
72: Explain three methods of transferring a table between two schema EXPORT-IMPORT
CREATE TABLE .. AS SELECT
COPY command

Oracle 11g Database New Features Interview Questions and Answers

1. Database Replay 2. The SQL Performance Analyzer 3. Online Patching in Oracle Database Control 4. Automatic Diagnostic Repository (ADR) 5. Data Recovery Advisor 6. Automatic Memory Management 7. Invisible Indexes 8. Read-Only Tables 9. Shrinking Temporary Tablespaces and Tempfiles
10. Server Result Cache
11. SQL Tuning Automation
12. SQL Plan Management
13. Database ADDM
14. New SYSASM Privilege for ASM Administration
15. Enhanced Block Media Recovery
16. VALIDATE Command
17. Configuring an Archived Redo Log Deletion Policy
18. Active Database Duplication
19. Virtual Private Catalogs
20. ASM Restricted Mode
21. Checking Diskgroup
22. The FORCE option with Drop Diskgroup Command
23. Active Data Guard is a new option for Oracle Database 11g Enterprise Edition

ASM Rolling Upgrades

Database Replay
Database Replay (sometimes named as Workload Replay) feature in Oracle11g allows you to reproduce the production database conditions in a testing environment.In other words, with this feature you can capture the actual workload on a production system and replay it in a test system. This way, you can analyze the condition of the production database without working on the actual production database.

This feature enables you to test the impact of applying changes on a production database. These changes could be database upgrades, switching to RAC, application upgrades, operating system upgrades or storage system changes.

The SQL Performance Analyzer
The SQL Performance Analyzer (SPA) aims at measuring the impact of applying any change on the database on the performance of the SQL statements execution. If it finds out performance degradation in one or more SQL statements, it provides you recommendations on how to improve their performance.

This is very useful for a DBA to analyze how a change on the database (including database upgrade) may affect the execution efficiency of SQL statements. Using this tool is explained here because you may consider using it to study the effect of upgrading an Oracle database 10g release 2 to 11g.

Note:
If you plan to use SPA on a test database, it is highly recommended to make the test database resemble the production database as closely as possible. You can use the RMAN duplicate command for this purpose.

Online Patching in Oracle Database Control
Patching through Database Control is enhanced in Oracle 11g. With Oracle 11g online patching (or called hot patching),you can apply or roll back a database patch while the instance is running. Also it can detect conflicts between two online patches.On the other hand, online patching consumes more memory than the conventional method.

In UNIX systems, you use the script $ORACLE_HOME/OPatch/opatch to invoke the online patching.

Automatic Diagnostic Repository (ADR)
The Automatic Diagnostic Repository (ADR) is a file system repository to store diagnostic data source such as alter log, trace files, user and background dump files, and also new types of troubleshooting files such as Health Monitor reports, Incident packages, SQL test cases and Data repair records.

In Oracle 11g, there is a new framework (named as fault diagnosability infrastructure) consisting of many tools for diagnosing and repairing the errors in the database. All those tools refer to the ADR in their operation.

ADR is developed to provide the following advantages:
1.Diagnosis data, because it is stored in file system, is available even when the database is down.
2.It is easier to provide Oracle support with diagnosis data when a problem occurs in the database.
3.ADR has diagnosis data not only for the database instance. It has troubleshooting data for other Oracle components such as ASM and CRS.

Note:
For each database instance two alert log files are generated: one as text file and one with xml format. Contents of the xml-formatted file can be examined using adrci tool.

Also the xml-formatted alert log is saved in the ADR and specifically in the directory
$ORACLE_BASE/diag/rdbms/$INSTANCE_NAME/$ORACLE_SID/alert

Data Recovery Advisor
Data Recovery Advisor is an Oracle Database 11g tool that automatically diagnoses data failures, determines and presents appropriate repair options,and executes repairs at the user's request. Data Recovery Advisor can diagnose failures such as the following:

1. Inaccessible components like datafiles and control files.
2. Physical corruptions such as block checksum failures and invalid block header
3. Field values
4. Inconsistent datafiles (online and offline)
5. I/O failures

The advisor however doe not recover from failures on standby databases or RAC environment. This advisor can be used through RMAN or the Enterprise Manager.

Automatic Memory Management
In Oracle 11g, a new parameter named as MEMORY_TARGET is added to automate memory allocation for both the SGA and PGA. When this parameter is set, the SGA and the PGA memory sizes are automatically determined by the instance based on the database workload.

This parameter is dynamic and can be alter using the ALTER SYSTEM command as shown below:
ALTER SYSTEM SET MEMORY_TARGET = 1024M ;

However, if the database is not configured to use this parameter and you want to use it, you must restart the database after setting the parameter.

Invisible Indexes
Invisible index is an index that is not considered by the optimizer when creating the execution plans. This can be used to test the effect of adding an index to a table on a query (using index hint) without actually being used by the other queries.

When using invisible indexes, consider the following:
- If you rebuild an invisible index, the resulting operation will make the index visible.
- If you want the optimizer to consider the invisible indexes in its operation, you can set the new initialization parameter OPTIMIZER_USE_INVISIBLE_INDEXES to TRUE (the default is FALSE). You can set the parameter in the system and session levels.

Read-Only Tables
In Oracle 11g, you can set a table to be read only, i.e. users can only query from the table but no DML statement is allowed on the table.

Shrinking Temporary Tablespaces and Tempfiles
In Oracle 11g, you can shrink temporary tablespaces and tempfiles.

Server Result Cache
In Oracle 11g, there is a new SGA component called result cache, which is used cache SQL query and PL/SQL function results. The database serves the results for the executed SQL queries and PL/SQL functions from the cache instead of re-executing the actual query. Of course,the target is to obtain high response time. The cached results stored become invalid when data in the dependent database objects is modified.

As clear from its concept, result cache is mostly useful in for frequently executed queries with rare changes on the retrieved data.

SQL Tuning Automation
The SQL Tuning Advisor is run by default every night during the automated maintenance window. Basically, the advisor catches the SQL statements from AWR that are candidate for tuning (they are called buckets) during four different time periods.It then automatically creates SQL profile for any poor SQL statement, if that helps. Tuned plans are automatically added to the SQL plan baselines by the automatic SQL tuning task.

The advisor also may recommend actions like creating new indexes, refreshing statistics or re-writing the statement. These actions, however, are not automatically implemented by the advisor.

On Oracle 11g Release 2 (11.2.0.2), a new package named as DBMS_AUTO_SQLTUNE should be used instead of the DBMS_SQLTUNE package. The new package provides more restrictive access to the Automatic SQL Tuning feature.

To use the DBMS_AUTO_SQLTUNE package, you must have the DBA role, or have EXECUTE privileges granted by an administrator. The only exception is the EXECUTE_AUTO_TUNING_TASK procedure, which can only be run by SYS.

SQL Plan Management
SQL plan management (SPM), is a new feature in Oracle 11g that prevents performance regressions resulting from sudden changes to the execution plan of a SQL statement by providing components for capturing, selecting, and evolving SQL plan information.Changes to the execution plan may be resulted from database upgrades,system and data changes, application upgrade or bug fixes.

When SPM is enabled, the system maintains a plan history that contains all plans generated by the optimizer and store them in a component called plan baseline. Among the plan history in the plan baseline, plans that are verified not to cause performance regression are marked as acceptable. The plan baseline is used by the optimizer to decide on the best plan to use when compiling a SQL statement.

Repository stored in data dictionary of plan baselines and statement log maintained by the optimizer is called
SQL management base(SMB).

SQL Plan management is implemented by undertaking the following phases:
1.Capturing SQL Plan Baselines: this can be done automatically or manually.
2.Selecting SQL Plan Baselines by the optimizer
3.Evolving SQL Plan Baselines

Database ADDM
Oracle Database 11g has added a new layer of analysis to ADDM called Database ADDM. The mode ADDM was working in Oracle 10g is now called instance ADDM. The main target of database ADDM is to analyze and report on RAC environment. To enable Database ADDM, you set the parameter INSTANCES in DBMS_ADVISOR.

New SYSASM Privilege for ASM Administration
SYSASM is a new privilege introduced in Oracle 11g. Users who are granted this privilege can perform ASM administration tasks. The idea behind this privilege is to separate database management and the storage management responsibilities.

Backup and Recovery New Features:-

Enhanced Block Media Recovery
In Oracle Database 11g, there is a new command to perform block media recovery, named the recover ... blockcommand replacing the old blockrecover command. The new command is more efficient since because it searches the flashback logs for older uncorrupted versions of the corrupt blocks. This requires the database to work in archivelog mode and has the Database Flashback enabled.

While the block media recovery is going on, any attempt by users to access data in the corrupt blocks will result in an error message, telling the user that the data block is corrupt.

VALIDATE Command
You can use the new command VALIDATE to manually check for physical and logical corruptions in datafiles,backup sets, and even individual data blocks. The comma nd by default checks for physical corruption. You can optionally specify CHECK LOGICAL . Corrupted blocks are reported in V$DATABASE_BLOCK_CORRUPTION.

Configuring an Archived Redo Log Deletion Policy
You can use RMAN to create a persistent configuration that controls when archived redo logs are eligible for deletion from disk or tape. This deletion policy applies to all archiving destinations, including the flash recovery area. When the policy is configured, it applies on the automatic deletion of the logs in the flash recovery area and the manual deletion by the BACKUP ... DELETE and DELETE ... ARCHIVELOG commands.

To enable an archived redo log deletion policy, run the CONFIGURE ARCHIVELOG DELETION POLICY BACKED UP n TIMES command with the desired options.

Active Database Duplication
In Oracle Database 11g, you can directly duplicate a data base over the network without having to back up and provide the source database files. This direct database duplication is called active database duplication. It can be done either with Database Control or through RMAN. Instance that runs the duplicated database is called auxiliary instance.

Virtual Private Catalogs
In Oracle Database 11g, you can restrict access to the recovery catalog by granting access to only a subset of the metadata in the recovery catalog. The subset that a user has read/write access to is termed as virtual private catalog, or just virtual catalog. The central or source recovery catalog is now called the base recovery catalog.

ASM Restricted Mode

In Oracle 11g, you can start the ASM instance in restricted mode. When in restricted mode, databases will not be permitted to access the ASM instance. Also, individual diskgroup can be set in restricted mode.

Checking Diskgroup

Starting from Oracle Database 11g, you can validate the internal consistency of ASM diskgroup metadata using the ALTER DISKGROUP ... CHECK command. Summary of errors is logged in the ASM alert log file.

The FORCE option with Drop Diskgroup Command

If a disk is destroyed beyond repair, you want to drop it. But because the disk is practically damaged, you cannot mount it and thus you cannot issue the DROP DISKGROUP command against it. In such a condition, Oracle 11g provides the FORCE INCLUDING CONTENTS option to drop the diskgroup even if it is not mounted.

SQL>DROP DISKGROUP <DISKGROUP_NAME> FORCE INCLUDING CONTENTS;

ASM Rolling Upgrades
ASM rolling upgrades enable you to independently upgrade or patch clustered ASM nodes without affecting database availability, thus providing greater uptime. Rolling upgrade means that all of the features of a clustered ASM environment function when one or more of the nodes in the cluster use different software versions.

Active Data Guard is a new option for Oracle Database 11g Enterprise Edition
An Active Data Guard standby database is an exact copy of the primary that is open read-only while it continuously applies changes transmitted by the primary database. An active standby can offload ad-hoc queries, reporting, and fast incremental backups from the primary database, improving performance and scalability while preventing data loss or downtime due to data corruptions, database and site failures, human error, or natural disaster. Oracle Active Data Guard enables read-only access to a physical standby database.

With Oracle Active Data Guard, a physical standby database can be used for real-time reporting, with minimal latency between reporting and production data. Compared with traditional replication methods, Active Data Guard is very simple to use, transparently supports all datatypes, and offers very high performance. Oracle Active Data Guard also allows backup operations to be off-loaded to the standby database, and be done very fast using intelligent incremental backups.

Active Dataguard Features:
1. Physical Standby with Real-time Query
2. Fast Incremental Backup on Physical Standby.
3. Automatic Block Repair.

http://ahmedbaraka.com/computer/docs/oracle_11g_nf_1.0.pdf

http://pocketoracle.blogspot.com/search/label/10g%20New%20Features

http://pocketoracle.blogspot.com/search/label/11g%20New%20Features

Oracle RAC Interview Questions and Answers

1. What is the use of RAC?
RAC stands for Real Application Clusters. It allows multiple nodes in a clustered system to mount and open a single database that resides on shared disk storage. Should a single system (node) fail, the database service will still be available on the remaining nodes. A non-RAC database is only available on a single system. If that system fails, the database service will be down (single point of failure).
The main aim of Oracle RAC is to implement a clustered database to provide performance, scalability and resilience.

2. What are the prerequisites for RAC setup? 1. Identical server and OS (same version with necessary packages) a. Procure certified hardware b. Storage requirement (SAN, NAS) c. Memory requirement (RAM) d. Network requirement (2 NIC’s) 2. Add IP address in hosts files (Public,Private, VIP and SCAN) 3. Operating system requirements (both nodes should be same kernel version) e. Swap space, Temp space f. Sync.system clocks g. Check package version h. Disable SELinux, host firewall, i. Set kernel parameters j. Configure public, private , vip network interface on each node. 4. Create dba group and user(oracle software owner) for oracle installation 5. Create necessary directories for installation. k. Allocate a local disk mount point for the CRS_HOME, ASM_HOME, ORACLE_HOME l. Allocate 3 devices for the voting disk (This assumes an 11g clusterware installation) (11g clusterware can use block devices for the voting disk) (10gclusterware requires raw devices). m. Allocate 2 devices for the cluster registry (This assumes an 11g clusterware installation) (11g clusterware can use block devices for the voting disk) (10g clusterware requires raw devices). 6. ASM requirements. n. Download & install ASMLIB. o. Allocate ASM disks for your ASM Data disk group p. Create Disks for your Flash Recovery Area ASM disk group

7. Configure SSH (optional for 11g R2) 8. Set the environment variables. 9. Download oracle softwares (including Grid infrastructure and RDBMS ) 10. Verify using CLUVFY utility for pre-requisites for RAC setup. 11. X-windows for oracle installation GUI based

3. What are Oracle Clusterware/Daemon processes and what they do? ocssd, crsd, evmd, oprocd, racgmain, racgimon 4. What are the special background processes for RAC (or) what is difference in stand-alone database & RAC database background processes?
DIAG, LCKn, LMD, LMSn, LMON

5. What are structural changes in 11g R2 RAC?

http://satya-racdba.blogspot.com/2010/07/new-features-in-9i-10g-11g-rac.html

Grid & ASM are on one home, Voting disk & OCRfile can be on the ASM, SCAN, By using srvctl, we can mange diskgroups, home, ons, eons, filesystem, srvpool, server, scan, scan_listener, gns, vip, oc4j, GSD

Additional:
New features in Oracle 9i/10g/11g RAC
Oracle 9i RAC * OPS (Oracle Parallel Server) was renamed as RAC * CFS (Cluster File System) was supported * OCFS (Oracle Cluster File System) for Linux and Windows * watchdog timer replaced by hangcheck timer

Oracle 10g R1 RAC * Cluster Manager replaced by CRS * ASM introduced * Concept of Services expanded * ocrcheck introduced * ocrdump introduced * AWR was instance specific

Oracle 10g R2 RAC * CRS was renamed as Clusterware * asmcmd introduced * CLUVFY introduced * OCR and Voting disks can be mirrored * Can use FAN/FCF with TAF for OCI and ODP.NET

Oracle 11g R1 RAC * Oracle 11g RAC parallel upgrades - Oracle 11g have rolling upgrade features whereby RAC database can be upgraded without any downtime. * Hot patching - Zero downtime patch application. * Oracle RAC load balancing advisor - Starting from 10g R2 we have RAC load balancing advisor utility. 11g RAC load balancing advisor is only available with clients who use .NET, ODBC, or the Oracle Call Interface (OCI). * ADDM for RAC - Oracle has incorporated RAC into the automatic database diagnostic monitor, for cross-node advisories. The script addmrpt.sql run give report for single instance, will not report all instances in RAC, this is known as instance ADDM. But using the new package DBMS_ADDM, we can generate report for all instances of RAC, this known as database ADDM. * Optimized RAC cache fusion protocols - moves on from the general cache fusion protocols in 10g to deal with specific scenarios where the protocols could be further optimized. * Oracle 11g RAC Grid provisioning - The Oracle grid control provisioning pack allows us to "blow-out" a RAC node without the time-consuming install, using a pre-installed "footprint".

Oracle 11g R2 RAC * We can store everything on the ASM. We can store OCR & voting files also on the ASM. * ASMCA * Single Client Access Name (SCAN) - eliminates the need to change tns entry when nodes are added to or removed from the Cluster. RAC instances register to SCAN listeners as remote listeners. SCAN is fully qualified name. Oracle recommends assigning 3 addresses to SCAN, which create three SCAN listeners. * Clusterware components: crfmond, crflogd, GIPCD. * AWR is consolidated for the database. * 11g Release 2 Real Application Cluster (RAC) has server pooling technologies so it’s easier to provision and manage database grids. This update is geared toward dynamically adjusting servers as corporations manage the ebb and flow between data requirements for datawarehousing and applications. * By default, LOAD_BALANCE is ON. * GSD (Global Service Deamon), gsdctl introduced. * GPnP profile. * Cluster information in an XML profile. * Oracle RAC OneNode is a new option that makes it easier to consolidate databases that aren’t mission critical, but need redundancy. * raconeinit - to convert database to RacOneNode. * raconefix - to fix RacOneNode database in case of failure. * racone2rac - to convert RacOneNode back to RAC. * Oracle Restart - the feature of Oracle Grid Infrastructure's High Availability Services (HAS) to manage associated listeners, ASM instances and Oracle instances. * Oracle Omotion - Oracle 11g release2 RAC introduces new feature called Oracle Omotion, an online migration utility. This Omotion utility will relocate the instance from one node to another, whenever instance failure happens. * Omotion utility uses Database Area Network (DAN) to move Oracle instances. Database Area Network (DAN) technology helps seamless database relocation without losing transactions. * Cluster Time Synchronization Service (CTSS) is a new feature in Oracle 11g R2 RAC, which is used to synchronize time across the nodes of the cluster. CTSS will be replacement of NTP protocol. * Grid Naming Service (GNS) is a new service introduced in Oracle RAC 11g R2. With GNS, Oracle Clusterware (CRS) can manage Dynamic Host Configuration Protocol (DHCP) and DNS services for the dynamic node registration and configuration. * Cluster interconnect: Used for data blocks, locks, messages, and SCN numbers. * Oracle Local Registry (OLR) - From Oracle 11gR2 "Oracle Local Registry (OLR)" something new as part of Oracle Clusterware. OLR is node’s local repository, similar to OCR (but local) and is managed by OHASD. It pertains data of local node only and is not shared among other nodes. * Multicasting is introduced in 11gR2 for private interconnect traffic. * I/O fencing prevents updates by failed instances, and detecting failure and preventing split brain in cluster. When a cluster node fails, the failed node needs to be fenced off from all the shared disk devices or diskgroups. This methodology is called I/O Fencing, sometimes called Disk Fencing or failure fencing. * Re-bootless node fencing (restart)‏ - instead of fast re-booting the node, a graceful shutdown of the stack is attempted. * Clusterware log directories: acfs* * HAIP (IC VIP). * Redundant interconnects: NIC bonding, HAIP. * RAC background processes: DBRM – Database Resource Manager, PING – Response time agent. * Virtual Oracle 11g RAC cluster - Oracle 11g RAC supports virtualization.

6. What are the new features in 11g (R2) RAC?

http://satya-racdba.blogspot.com/2010/07/new-features-in-9i-10g-11g-rac.html * We can store everything on the ASM. We can store OCR & voting files also on the ASM. * ASMCA * Single Client Access Name (SCAN) - eliminates the need to change tns entry when nodes are added to or removed from the Cluster. RAC instances register to SCAN listeners as remote listeners. SCAN is fully qualified name. Oracle recommends assigning 3 addresses to SCAN, which create three SCAN listeners. * Clusterware components: crfmond, crflogd, GIPCD. * AWR is consolidated for the database. * 11g Release 2 Real Application Cluster (RAC) has server pooling technologies so it’s easier to provision and manage database grids. This update is geared toward dynamically adjusting servers as corporations manage the ebb and flow between data requirements for datawarehousing and applications. * By default, LOAD_BALANCE is ON. * GSD (Global Service Deamon), gsdctl introduced. * GPnP profile. * Cluster information in an XML profile. * Oracle RAC OneNode is a new option that makes it easier to consolidate databases that aren’t mission critical, but need redundancy. * raconeinit - to convert database to RacOneNode. * raconefix - to fix RacOneNode database in case of failure. * racone2rac - to convert RacOneNode back to RAC. * Oracle Restart - the feature of Oracle Grid Infrastructure's High Availability Services (HAS) to manage associated listeners, ASM instances and Oracle instances. * Oracle Omotion - Oracle 11g release2 RAC introduces new feature called Oracle Omotion, an online migration utility. This Omotion utility will relocate the instance from one node to another, whenever instance failure happens. * Omotion utility uses Database Area Network (DAN) to move Oracle instances. Database Area Network (DAN) technology helps seamless database relocation without losing transactions. * Cluster Time Synchronization Service (CTSS) is a new feature in Oracle 11g R2 RAC, which is used to synchronize time across the nodes of the cluster. CTSS will be replacement of NTP protocol. * Grid Naming Service (GNS) is a new service introduced in Oracle RAC 11g R2. With GNS, Oracle Clusterware (CRS) can manage Dynamic Host Configuration Protocol (DHCP) and DNS services for the dynamic node registration and configuration. * Cluster interconnect: Used for data blocks, locks, messages, and SCN numbers. * Oracle Local Registry (OLR) - From Oracle 11gR2 "Oracle Local Registry (OLR)" something new as part of Oracle Clusterware. OLR is node’s local repository, similar to OCR (but local) and is managed by OHASD. It pertains data of local node only and is not shared among other nodes. * Multicasting is introduced in 11gR2 for private interconnect traffic. * I/O fencing prevents updates by failed instances, and detecting failure and preventing split brain in cluster. When a cluster node fails, the failed node needs to be fenced off from all the shared disk devices or diskgroups. This methodology is called I/O Fencing, sometimes called Disk Fencing or failure fencing. * Re-bootless node fencing (restart)‏ - instead of fast re-booting the node, a graceful shutdown of the stack is attempted. * Clusterware log directories: acfs* * HAIP (IC VIP). * Redundant interconnects: NIC bonding, HAIP. * RAC background processes: DBRM – Database Resource Manager, PING – Response time agent. * Virtual Oracle 11g RAC cluster - Oracle 11g RAC supports virtualization. Grid & ASM are on one home, Voting disk & ocrfile can be on the ASM,SCAN, By using srvctl, we can mange diskgroups, home, ons, eons, filesystem, srvpool, server, scan, scan_listener, gns, vip, oc4j,GSD
7. What is cache fusion?
Transfers of data block between RAC instances by using private network. Cache Fusion is the remote memory mapping of Oracle buffers, shared between the caches of participating nodes in the cluster. When a block of data is read from datafile by an instance within the cluster and another instance is in need of the same block, it is easy to get the block image from the instance which has the block in its SGA rather than reading from the disk.

8. What is the purpose of Private Interconnect?
Clusterware uses the private interconnect for cluster synchronization (network heartbeat) and daemon communication between the clustered nodes. This communication is based on the TCP protocol. RAC uses interconnect for cache fusion (UDP) and inter-process communication (TCP).

9. What are the Clusterware components?
Voting Disk - Oracle RAC uses the voting disk to manage cluster membership by way of a health check and arbitrates cluster ownership among the instances in case of network failures. The voting disk must reside on shared disk.
Oracle Cluster Registry (OCR) - Maintains cluster configuration information as well as configuration information about any cluster database within the cluster. The OCR must reside on shared disk that is accessible by all of the nodes in your cluster. The daemon OCSSd manages the configuration info in OCR and maintains the changes to cluster in the registry.

Virtual IP (VIP) - When a node fails, the VIP associated with it is automatically failed over to some other node and new node re-arps the world indicating a new MAC address for the IP. Subsequent packets sent to the VIP go to the new node, which will send error RST packets back to the clients. This results in the clients getting errors immediately. crsd – Cluster Resource Services Daemon cssd – Cluster Synchronization Services Daemon evmd – Event Manager Daemon oprocd / hangcheck_timer – Node hang detector

10. What is OCR file?
The OCR also manages information about Oracle Clusterware resource profiles for customized applications. Maintains cluster configuration information as well as configuration information about any cluster database within the cluster. The OCR must reside on shared disk that is accessible by all of the nodes in your cluster. The daemon OCSSd manages the configuration info in OCR and maintains the changes to cluster in the registry.

11. What is Voting file/disk and how many files should be there?
Voting Disk File is a file on the shared cluster system or a shared raw device file. Oracle Clusterware uses the voting disk to determine which instances are members of a cluster. Voting disk is akin to the quorum disk, which helps to avoid the split-brain syndrome. Oracle RAC uses the voting disk to manage cluster membership by way of a health check and arbitrates cluster ownership among the instances in case of network failures. The voting disk must reside on shared disk.

12. How to take a backup of OCR file?
#ocrconfig -manualbackup
#ocrconfig -export file_name.dmp
#ocrdump -backupfile my_file
$cp -p -R /u01/app/crs/cdata /u02/crs_backup/ocrbackup/RAC1

13. How to recover OCR file?
#ocrconfig -restore backup_file.ocr
#ocrconfig -import file_name.dmp

14. What is local OCR (OLR)?
From 11gR2 Oracle introduced “Oracle Local Registry(OLR)”, something new as part of Oracle Clusterware.OLR is node’s local repository,similar to OCR (but local) and is managed by OHASD.It pertains data of local node only and is not shared among other nodes.On a linux environment the configuration file is placed in /etc/oracle location.
The OLR dump shows that it contains data about ORA_CRS_HOME, localhost version, activeversion, GPnP details, OCR latest backup time and location information about OCR daily, weekly backup location and node name etc.This formation stored in the OLR is needed by OHASD to start or join a cluster.When the crs is started using crsctl start crs command , the alert<hostname>.log in GRID_HOME/log/<hostname>/ shows –
/etc/oracle/local.ocr
/var/opt/oracle/local.ocr

15. How to check backup of OCR files?
#ocrconfig –showbackup

16. How to take backup of voting file?
Ans:
dd if=/u02/ocfs2/vote/VDFile_0 of=$ORACLE_BASE/bkp/vd/VDFile_0 crsctl backup css votedisk -- from 11g R2

17. How do I identify the voting disk location?
Ans:
# crsctl query css votedisk

18. How do I identify the OCR file location? check /var/opt/oracle/ocr.loc or /etc/ocr.loc
Ans:
# ocrcheck

19. If voting disk/OCR file got corrupted and don’t have backups, how to get them?
Ans:
if voting disk,We have to install Clusterware.
If OCR, we need re-execute root.sh (workaround)

20. Who will manage OCR files?
Ans:
cssd will manage OCR.

21. Who will take backup of OCR files?
Ans:
crsd will take backup.

22. What is split brain syndrome?
Will arise when two or more instances attempt to control a cluster database. In a two-node environment, one instance attempts to manage updates simultaneously while the other instance attempts to manage updates.

23. What are various IPs used in RAC? Or How may IPs we need in RAC?

Public IP, Private IP, Virtual IP, SCAN IP ( each 2 IP and SCAN 3 IP for 2 node RAC)

24. What is the use of virtual IP?
When a node fails, the VIP associated with it is automatically failed over to some other node and new node re-arps the world indicating a new MAC address for the IP. Subsequent packets sent to the VIP go to the new node, which will send error RST packets back to the clients. This results in the clients getting errors immediately.

Without using VIPs or FAN, clients connected to a node that died will often wait for a TCP timeout period (which can be up to 10 min) before getting an error. As a result, you don't really have a good HA solution without using VIPs.

25. What is the use of SCAN IP (SCAN name) and will it provide load balancing?
Single Client Access Name (SCAN) is a new Oracle Real Application Clusters (RAC) 11g Release 2, feature that provides a single name for clients to access an Oracle Database running in a cluster. The benefit is clients using SCAN do not need to change if you add or remove nodes in the cluster.

26. How many SCAN listeners will be running?

Three SCAN listeners only.

27. What is FAN?
Applications can use Fast Application Notification (FAN) to enable rapid failure detection, balancing of connection pools after failures, and re-balancing of connection pools when failed components are repaired. The FAN process uses system events that Oracle publishes when cluster servers become unreachable or if network interfaces fail.

28. What is FCF?
Fast Connection Failover provides high availability to FAN integrated clients, such as clients that use JDBC, OCI, or ODP.NET. If you configure the client to use fast connection failover, then the client automatically subscribes to FAN events and can react to database UP and DOWN events. In response, Oracle gives the client a connection to an active instance that provides the requested database service.

29. What is TAF and TAF policies?
Transparent Application Failover (TAF) - A runtime failover for high availability environments, such as Real Application Clusters and Oracle Real Application Clusters Guard, TAF refers to the failover and re-establishment of application-to-service connections. It enables client applications to automatically reconnect to the database if the connection fails, and optionally resume a SELECT statement that was in progress. This reconnect happens automatically from within the Oracle Call Interface (OCI) library.

30. How will you upgrade RAC database? http://www.oracledba.org/upgrade/Upgrade_10gR2_RAC_to_11gR1_RAC.htm http://www.oracledba.org/upgrade/Upgrade_10gR2_RAC_to_11gR2_RAC.htm
The Upgrade Process is composed of below Stages:

1. Pre-Upgrade Tasks 2. Hide the 10gR2 Clusterware installation. 3. Install 11gR2 Grid Infrastructure. 4. Move 10gR2 ASM Diskgroups to 11gR2 Grid Infrastructure. 5. Register10gR2 RAC database and services to 11gR2 Grid Infrastructure. 6. Install 11gR2 RAC for database home. 7. Manually upgrade original 10gR2 RAC database to 11gR2 RAC. 1. Install the 11gR2 RAC database software 2. Move the Listener LAB_LISTENER to 11gR2 RAC Home. 3. Start Manual Process to upgrade the original labdb database from 10gR2 RAC to 11gR2 RAC.

Pre-Upgrade tasks:

* Install/Upgrade RPMs required for 11gR2 RAC Installation * Add SCAN VIPs to the DNS * Setup of Network Time Protocol * Start the nscd on all the RAC nodes * Create 3 ASM Disks for 11gR2 OCR and Voting Disks. * Backing up 10gR2 existing HOMEs and database

31. What are rolling patches and how to apply?
"The term rolling upgrade refers to upgrading different databases or different instances of the same database (in a Real Application Clusters environment) one at a time, without stopping the database.
The advantage of a RAC rolling upgrade is that it enables at least some instances of the RAC installation to be available during the scheduled outage required for patch upgrades. Only the RAC instance that is currently being patched needs to be brought down. The other instances can continue to remain available. This means that the impact on the application downtime required for such scheduled outages is further minimized. Oracle's opatch utility enables the user to apply the patch successively to the different instances of the RAC installation.
Rolling upgrade is available only for patches that have been certified by Oracle to be eligible for rolling upgrades. Typically, patches that can be installed in a rolling upgrade include:

• Patches that do not affect the contents of the database such as the data dictionary
• Patches not related to RAC internode communication
• Patches related to client-side tools such as SQL*PLUS, Oracle utilities, development libraries, and Oracle Net
• Patches that do not change shared database resources such as datafile headers, control files, and common header definitions of kernel modules
• Rolling upgrade of patches is currently available for one-off patches only. It is not available for patch sets.
Rolling patch upgrades are not available for deployments where the Oracle Database software is shared across the different nodes. This is the case where the Oracle home is on Cluster File System (CFS) or on shared volumes provided by file servers or NFS-mounted drives. The feature is only available where each node has its own copy of the Oracle Database software."

1. Ensure that your Oracle Database installation is the same release for which you are applying this patch 2. Shut down the instance on one node. 3. Shut down all nodeapps services on the node in step 1: 4. srvctl stop nodeapps -n <node-name> 5. Apply the patch on the node in step 1. a. Set your current directory to the directory where the patch is located and then run the OPatch utility by entering the following commands: i. unzip p8576156_10204_Linux-x86.zip ii. cd 8576156 iii. opatch apply 6. Start the instance on the node in step 1. 7. Start all nodeapps services on the node in step 1: 8. srvctl start nodeapps -n <node-name> 9. Shut down the instance on the next node. 10. Repeat steps 1-6 on all the nodes in the cluster. 11. Post installation instruction : b. Execute SQL> @catbundle.sql psu apply c. SQL> @utlrp.sql http://www.appsdba.info/docs/RAC/install/Rolling_Upgrade_Apply_patch.pdf 32. How to add/remove a node? * Oracle RAC – adding and removing cluster nodes * Part I
Node addition * Methods * Silent cloning procedures * Enterprise Manager Grid Control cloning and adding instance * addNode.sh and DBCA * Manual * Steps * Setup hardware for a new node * Install and configure OS * Configure account equivalency * Add Oracle Clusterware to the new node * Configure ONS for the new node * Add ASM and DB home to the new node * Configure a listener on the new node * Add an ASM and a database instances * Hardware setup * New node of the cluster should be: * of similar type as other cluster nodes (the same architecture e.g. x86_64) * of similar size to other cluster nodes * physically connected to the shared storage used by the cluster * physically connected to the cluster private network(s) * OS installation and configuration * Install OS on the new node * The same flavor and version as installed on other nodes (e.g. RHEL 4.0) * The same kernel version recommended * Make sure that all required packages are installed * Ideally the list of software packages should be identical on all cluster nodes * Configure kernel parameters and shell limits * Create Oracle-related OS groups and users * Configure network interfaces * On one of the old cluster nodes edit /etc/hosts file adding entries related to the new node; distribute this file to all cluster nodes * Configure hangcheck timer module * Account equivalency * Passwordless access from one Oracle software owner account to another has to be configured * Needed only during software installation * The easiest is to re-configure the equivalency for the whole cluster * Use sshUserSetup.sh script available on metalink * Adding Oracle Clusterware and configuring ONS * Run addNode.sh script from an existing cluster node * Adding ASM and DB home (addNode script) * Depending on the chosen configuration can be done in either 1 or 2 steps * Run addNode script on an existing cluster node * Adding ASM and DB home (cloning) * Go to an existing cluster node and tar ORACLE_HOME directory * Listener configuration * From the new node run netca to configure a listener: * Choose ‘Cluster configuration’ * Select the new node only * Choose ‘Listener configuration’ * Choose ‘Add’ * Leave the default listener name * Leave intact the default protocol choice * Specify proper port * Complete the configuration * Check with the crs_stat command if the new listener has been registered to clusterware * Edit listener.ora and tnsnames.ora files on the new node: * You may want to remove extproc related entries * In tnsnames.ora add/edit entries related to the new listener * Distribute updated tnsnames.ora file to all nodes of the cluster * Adding ASM and database instances (with DBCA) * Although this procedure is recommended by Oracle we have seen that it is quite unreliable and therefore we strongly recommend using manual procedure described later * Run DBCA from an old cluster node: * Choose ‘Oracle Real Application Clusters database’ * Choose ‘Instance Management’ * Choose ‘Add an instance’ * Specify SYS username and password * Select name of the new node * Modify custom service definitions * Agree to extend ASM to the new node * Complete the operation * Adding ASM and database instances (manually) * Edit /etc/oratab file on the new node * add entries describing new ASM and DB instances * Create dump directories for ASM and DB instances as defined by initialization parameters * Create ASM pfile in the default location ($ORACLE_HOME/dbs) * Create a password file for ASM * Adding ASM and database instances (manually) (2) * Connect to an existing database instance * Create an undo tablespace and a redo log thread for the new RAC node * Set properly init parameters specific to the new instance * Adding ASM and database instances (manually) (3) * Define clusterware targets related to the new database instance * Final steps * Install OEM agent * Redefine services if needed * Part II
Node removal * Steps * Stop and delete the DB instance on the node to be deleted * Clean up the ASM instance * Remove the listener from the node to be deleted * Remove RAC and ASM software from oraInventory * Remove ONS configuration from the node * Remove the node from the clusterware * Deleting DB instance on the node to be deleted from the cluster * Redefine services in a way that they do not use the node being deleted (using srvctl tool) * From the node that is not being deleted run DBCA: * Choose ‘Oracle Real Application Clusters database’ * Choose ‘Instance Management’ * Choose ‘Delete an instance’ * Provide SYS credentials * Select the instance to delete * Proceed with the deletion * Verify with the crs_stat command that the instance has been removed from the cluster registry * Cleaning up the ASM instance * Stop the ASM instance * Removing the listener * Run netca on the node being deleted: * Choose ‘Cluster configuration’ * Select the node being deleted * Choose ‘Listener configuration’ * Choose ‘Delete’ * Complete the deletion * Check with crs_stat tool if the listener has disappeared from OCR * Removing database software * Update oraInventory on the node being removed * Removing ONS configuration and cluster software * Remove ONS configuration * Removing cluster software (2) * Update oraInventory on the node being removed * Final steps (optional) * Remove binaries left on the removed node * Deconfigure OS oracle account equivalency * Stop and remove OEM agent from the node * Deconfigure private network interfaces

33. What are nodeapps?
Ans:
Nodeapps are a standard set of Oracle application services that are automatically launched for RAC (Real Application Cluster). The following services are lunched by nodeapps: * Virtual IP (VIP) * Oracle Net Listener * Global Services Daemon (GSD) * Oracle Notification Service (ONS) * Nodeapp services run on each node Can be relocated to other nodes through the virtual IP.

34. What is gsd (Global Service Daemon)?
The Global Services Daemon (GSD) runs on each node with one GSD process per node. The GSD coordinates with the cluster manager to receive requests from clients such as the DBCA, EM, and the SRVCTL utility to execute administrative job tasks such as instance startup or shutdown. The GSD is not an Oracle instance background process and is therefore not started with the Oracle instance.

35. How to do load balancing in RAC?
Client Side Connect-Time Load Balance
The client load balancing feature enables clients to randomize connection requests among the listeners.
This is done by client Tnsnames Parameter: LOAD_BALANCE.
The (load_balance=yes) instructs SQLNet to progress through the list of listener addresses in the address_list section of the net service name in a random sequence. When set to OFF, instructs SQLNet to try the addresses sequentially until one succeeds.

Client Side Connect-Time failover

This is done by client Tnsnames Parameter: FAILOVER
The (failover=on) enables clients to connect to another listener if the initial connection to the first listener fails. Without connect-time failover, Oracle Net attempts a connection with only one listener.

Server Side Listener Connection Load Balancing.

With server-side load balancing, the listener directs a connection request to the best instance currently providing the service.
Init parameter remote_listener should be set. When set, each instance registers with the TNS listeners running on all nodes within the cluster.

There are two types of server-side load balancing:
Load Based — Server side load balancing redirects connections by default depending on node load. This id default.
Session Based — Session based load balancing takes into account the number of sessions connected to each node and then distributes the connections to balance the number of sessions across the different nodes.

From 10g release 2 the service can be setup to use load balancing advisory. This mean connections can be routed using SERVICE TIME and THROUGHPUT. Connection load balancing means the goal of a service can be changed, to reflect the type of connections using the service.

36. What are the uses of services? How to find out the services in cluster?
Ans:
Applications should use the services to connect to the Oracle database. Services define rules and characteristics (unique name, workload balancing, failover options, and high availability) to control how users and applications connect to database instances.

37. How to find out the nodes in cluster (or) how to find out the master node?
Ans:
# olsnodes -- Which ever displayed first, is the master node of the cluster.
Select MASTER_NODE from v$ges_resource;
To find out which is the master node, you can see ocssd.log file and search for "master node number".

38. How to know the public IPs, private IPs, VIPs in RAC?
Ans:
# olsnodes -n -p -i node1-pub 1 node1-prv node1-vip node2-pub 2 node2-prv node2-vip

39. What utility is used to start DB/instance?
Ans:
srvctl start database –d database_name srvctl start instance –d database_name –i instance_name

40. How can you shutdown single instance?
Ans:
Change cluster_database=false srvctl stop instance –d database_name –i instance_name
41. What is HAS (High Availability Service) and the commands?
Ans:
HAS includes ASM & database instance and listeners. crsctl check has crsctl config has crsctl disable has crsctl enable has crsctl query has releaseversion crsctl query has softwareversion crsctl start has crsctl stop has [-f]

42. How many nodes are supported in a RAC Database?
Ans:
10g Release 2, support 100 nodes in a cluster using Oracle Clusterware, and 100 instances in a RAC database.

43. What is fencing?
Ans:
I/O fencing prevents updates by failed instances, and detecting failure and preventing split brain in cluster. When a cluster node fails, the failed node needs to be fenced off from all the shared disk devices or diskgroups. This methodology is called I/O Fencing, sometimes called Disk Fencing or failure fencing.

44. Why Clusterware installed in root (why not oracle)?

45. What are the wait events in RAC?
Ans:
http://satya-racdba.blogspot.com/2012/10/wait-events-in-oracle-rac-wait-events.html

gc buffer busy => specifies the time the remote instance locally spends accessing the requested data block. Caused may be because of not enough memory on your nodes, overloaded interconnect. gc buffer busy acquire gc current request gc cr request => the time it takes to retrieve the data from the remote cache. Oracle may not pick private interconnect and instead route traffic over slower public network. RAC event similar to buffer busy waits, tune SQL to request less data, tune network latency between RAC nodes, localize data access. gc cr failure gc current block lost => Lost blocks due to Interconnect or CPU. Indicates interconnect issues and contention. gc cr block lost => Lost blocks due to Interconnect or CPU. Indicates interconnect issues and contention. gc current block corrupt gc cr block corrupt gc current block busy => The consistent read request was delayed, most likely an I/O bottleneck. Block is already involved in GC operation, shows hot blocks or congestion. gc cr block busy => The consistent read request was delayed, most likely an I/O bottleneck. Blocks are busy in another instance, check for block level contention or hot blocks. gc current block congested => Long run queues and/or paging due to memory deficiency. Current block congestion, check for hot blocks or busy interconnect. gc cr block congested => Long run queues and/or paging due to memory deficiency. cr block congestion, check for hot blocks or busy interconnect. gc current block 2-way => Blocks are busy in another instance, check for block level contention or hot blocks. gc cr block 2-way => Blocks are busy in another instance, check for block level contention or hot blocks. gc current block 3-way => Blocks are busy in another instance, check for block level contention or hot blocks. gc cr block 3-way => Blocks are busy in another instance, check for block level contention or hot blocks.
(gc current/cr block n-way, n is number of nodes) gc current grant 2-way gc cr grant 2-way gc current grant busy gc current grant congested gc cr grant congested gc cr multi block read gc current multi block request => Full table or index scans. gc cr multi block request => Full table or index scans. gc cr block build time gc current block flush time gc cr block flush time gc current block send time gc cr block send time gc current block pin time gc domain validation gc current retry ges inquiry response gcs log flush sync

46. What is the difference between cr block and cur (current) block?
The difference between the current block and the CR block. The current block contains changes for all the committed and yet-to-be-committed transactions. A consistent read (CR) block represents a consistent snapshot of the data from a previous point in time. Applying undo/rollback segment information produces consistent read versions. Thus, a single data block can reside in many buffer caches under shared resources with different versions.

47. What are the initialization parameters that must have same value for every instance in an Oracle RAC database?
Ans:
http://satya-racdba.blogspot.com/2012/09/init-parameters-in-oracle-rac.html

ACTIVE_INSTANCE_COUNT
ARCHIVE_LAG_TARGET
COMPATIBLE
CLUSTER_DATABASE
CLUSTER_DATABASE_INSTANCE
CONTROL_FILES
DB_BLOCK_SIZE
DB_DOMAIN
DB_FILES
DB_NAME
DB_RECOVERY_FILE_DEST
DB_RECOVERY_FILE_DEST_SIZE
DB_UNIQUE_NAME
INSTANCE_TYPE
PARALLEL_MAX_SERVERS
REMOTE_LOGIN_PASSWORD_FILE
UNDO_MANAGEMENT

48. What are the new features in Oracle RAC 12c?

New features in Oracle Clusterware 12c
Here are the new features in Oracle 12c RAC/Clusterware.

1. Oracle Flex ASM - This feature of Oracle Clusterware 12c claims to reduce per-node overhead of using ASM instance. Now the instances can use remote node ASM for any planned/unplanned downtime. ASM metadata requests can be converted by non-local instance of ASM.

2. ASM Disk Scrubbing - From RAC 12c, ASM comes with disk scrubbing feature so that logical corruptions can be discovered. Also Oracle 12c ASM can automatically correct this in normal or high redundancy diskgroups.

3. Oracle ASM Disk Resync & Rebalance enhancements.

4. Application Continuity (AC) - is transparent to the application and in-case the database or the infrastructure is unavailable, this new features which work on JDBC drivers, masks recoverable outages. This recovers database session beneath the application so that the outage actually appears to be delayed connectivity or execution. Transaction guard (improvements of Fast Application Notification).

5. IPv6 Support - Oracle RAC 12c now supports IPv6 for Client connectivity, Interconnect is still on IPv4.

6. Per Subnet multiple SCAN - RAC 12c, per-Subnet multiple SCAN can be configured per cluster.

7. Each RAC instance opens the Container Database (CDB) as a whole so that versions would be same for CDB as well as for all of the Pluggable Databases (PDBs). PDBs are also fully compatible with RAC.

8. Oracle installer will run root.sh script across nodes. We don't have to run the scripts manually on all RAC nodes.

9. new "ghctl" command for patching.

10. TAF is extended to DML transactions failover (insert/update/delete).

What are Oracle Clusterware processes for 10g on UNIX and Linux

Cluster Synchronization Services (ocssd) — Manages cluster node membership and runs as the oracle user; failure of this process results in cluster restart.

Cluster Ready Services (crsd) — The crs process manages cluster resources (which could be a database, an instance, a service, a Listener, a virtual IP (VIP) address, an application process, and so on) based on the resource's configuration information that is stored in the OCR. This includes start, stop, monitor and failover operations. This process runs as the root user

Event manager daemon (evmd) —A background process that publishes events that crs creates.

Process Monitor Daemon (OPROCD) —This process monitor the cluster and provide I/O fencing. OPROCD performs its check, stops running, and if the wake up is beyond the expected time, then OPROCD resets the processor and reboots the node. An OPROCD failure results in Oracle Clusterware restarting the node. OPROCD uses the hangcheck timer on Linux platforms.

RACG (racgmain, racgimon) —Extends clusterware to support Oracle-specific requirements and complex resources. Runs server callout scripts when FAN events occur.

What are Oracle database background processes specific to RAC

•LMS—Global Cache Service Process

•LMD—Global Enqueue Service Daemon

•LMON—Global Enqueue Service Monitor

•LCK0—Instance Enqueue Process

To ensure that each Oracle RAC database instance obtains the block that it needs to satisfy a query or transaction, Oracle RAC instances use two processes, the Global Cache Service (GCS) and the Global Enqueue Service (GES). The GCS and GES maintain records of the statuses of each data file and each cached block using a Global Resource Directory (GRD). The GRD contents are distributed across all of the active instances.

What are Oracle Clusterware Components

Voting Disk — Oracle RAC uses the voting disk to manage cluster membership by way of a health check and arbitrates cluster ownership among the instances in case of network failures. The voting disk must reside on shared disk.

Oracle Cluster Registry (OCR) — Maintains cluster configuration information as well as configuration information about any cluster database within the cluster. The OCR must reside on shared disk that is accessible by all of the nodes in your cluster

How do you troubleshoot node reboot

Please check metalink ...

Note 265769.1 Troubleshooting CRS Reboots
Note.559365.1 Using Diagwait as a diagnostic to get more information for diagnosing Oracle Clusterware Node evictions.

How do you backup the OCR

There is an automatic backup mechanism for OCR. The default location is : $ORA_CRS_HOME\cdata\"clustername"\

To display backups :
#ocrconfig -showbackup
To restore a backup :
#ocrconfig -restore

With Oracle RAC 10g Release 2 or later, you can also use the export command:
#ocrconfig -export -s online, and use -import option to restore the contents back.
With Oracle RAC 11g Release 1, you can do a manaual backup of the OCR with the command:
# ocrconfig -manualbackup

How do you backup voting disk

#dd if=voting_disk_name of=backup_file_name

How do I identify the voting disk location

#crsctl query css votedisk

How do I identify the OCR file location

check /var/opt/oracle/ocr.loc or /etc/ocr.loc ( depends upon platform) or #ocrcheck

Is ssh required for normal Oracle RAC operation ?

"ssh" are not required for normal Oracle RAC operation. However "ssh" should be enabled for Oracle RAC and patchset installation.

What is SCAN?

Single Client Access Name (SCAN) is s a new Oracle Real Application Clusters (RAC) 11g Release 2 feature that provides a single name for clients to access an Oracle Database running in a cluster. The benefit is clients using SCAN do not need to change if you add or remove nodes in the cluster.

Click here for more details from Oracle

What is the purpose of Private Interconnect ?

Clusterware uses the private interconnect for cluster synchronization (network heartbeat) and daemon communication between the the clustered nodes. This communication is based on the TCP protocol.
RAC uses the interconnect for cache fusion (UDP) and inter-process communication (TCP). Cache Fusion is the remote memory mapping of Oracle buffers, shared between the caches of participating nodes in the cluster.

Why do we have a Virtual IP (VIP) in Oracle RAC?

Without using VIPs or FAN, clients connected to a node that died will often wait for a TCP timeout period (which can be up to 10 min) before getting an error. As a result, you don't really have a good HA solution without using VIPs.
When a node fails, the VIP associated with it is automatically failed over to some other node and new node re-arps the world indicating a new MAC address for the IP. Subsequent packets sent to the VIP go to the new node, which will send error RST packets back to the clients. This results in the clients getting errors immediately.

What do you do if you see GC CR BLOCK LOST in top 5 Timed Events in AWR Report?

This is most likely due to a fault in interconnect network.
Check netstat -s if you see "fragments dropped" or "packet reassemblies failed" , Work with your system administrator find the fault with network.

How many nodes are supported in a RAC Database?

10g Release 2, support 100 nodes in a cluster using Oracle Clusterware, and 100 instances in a RAC database.

Srvctl cannot start instance, I get the following error PRKP-1001 CRS-0215, however sqlplus can start it on both nodes? How do you identify the problem?

Set the environmental variable SRVM_TRACE to true.. And start the instance with srvctl. Now you will get detailed error stack.

what is the purpose of the ONS daemon?

The Oracle Notification Service (ONS) daemon is an daemon started by the CRS clusterware as part of the nodeapps. There is one ons daemon started per clustered node.
The Oracle Notification Service daemon receive a subset of published clusterware events via the local evmd and racgimon clusterware daemons and forward those events to application subscribers and to the local listeners.

This in order to facilitate:

a. the FAN or Fast Application Notification feature or allowing applications to respond to database state changes.
b. the 10gR2 Load Balancing Advisory, the feature that permit load balancing accross different rac nodes dependent of the load on the different nodes. The rdbms MMON is creating an advisory for distribution of work every 30seconds and forward it via racgimon and ONS to listeners and applications.

How does OCSSD starts first if voting disk & OCR resides in ASM Diskgroups?
You might wonder how CSSD, which is required to start the clustered ASM instance, can be started if voting disks are stored in ASM?
This sounds like a chicken-and-egg problem: without access to the voting disks there is no CSS, hence the node cannot join the cluster.
But without being part of the cluster, CSSD cannot start the ASM instance.
To solve this problem the ASM disk headers have new metadata in 11.2: you can use kfed to read the header of an ASM disk containing a voting disk.
The kfdhdb.vfstart and kfdhdb.vfend fields tell CSS where to find the voting file. This does not require the ASM instance to be up.
Once the voting disks are located, CSS can access them and joins the cluster.

What is gsdctl in RAC? list gsdctl commands in Oracle RAC?
GSDCTL stands for Global Service Daemon Control, we can use gsdctl commands to start, stop, and obtain the status of the GSD service on any platform.

The options for gsdctl are:-
$ gsdctl start -- To start the GSD service
$ gsdctl stop -- To stop the GSD service
$ gsdctl stat -- To obtain the status of the GSD service

Log file location for gsdctl:
$ ORACLE_HOME/srvm/log/gsdaemon_node_name.log

What is RAC?
RAC stands for Real Application cluster.
It is a clustering solution from Oracle Corporation that ensures high availability of databases by providing instance failover, media failover features.
Oracle RAC is a cluster database with a shared cache architecture that overcomes the limitations of traditional shared-nothing and shared-disk approaches to provide a highly scalable and available database solution for all the business applications.
Oracle RAC provides the foundation for enterprise grid computing.

What is Oracle RAC One Node?
Oracle RAC one Node is a single instance running on one node of the cluster while the 2nd node is in cold standby mode. If the instance fails for some reason then RAC one node detect it and restart the instance on the same node or the instance is relocate to the 2nd node incase there is failure or fault in 1st node. The benefit of this feature is that it provides a cold failover solution and it automates the instance relocation without any downtime and does not need a manual intervention. Oracle introduced this feature with the release of 11gR2 (available with Enterprise Edition).

What is RAC and how is it different from non RAC databases?
Oracle Real Application clusters allows multiple instances to access a single database, the instances will be running on multiple nodes.
In Real Application Clusters environments, all nodes concurrently execute transactions against the same database.
Real Application Clusters coordinates each node's access to the shared data to provide consistency and integrity.

What are the advantages of RAC (Real Application Clusters)?
Reliability - if one node fails, the database won't fail
Availability - nodes can be added or replaced without having to shutdown the database
Scalability - more nodes can be added to the cluster as the workload increases

what is Oracle RAC One Node?
Oracle RAC one Node is a single instance running on one node of the cluster while the 2nd node is in cold standby mode. If the instance fails for some reason then RAC one node detect it and restart the instance on the same node or the instance is relocate to the 2nd node incase there is failure or fault in 1st node. The benefit of this feature is that it provides a cold failover solution and it automates the instance relocation without any downtime and does not need a manual intervention. Oracle introduced this feature with the release of 11gR2 (available with Enterprise Edition).

What is Cache Fusion?
Oracle RAC is composed of two or more instances. When a block of data is read from datafile by an instance within the cluster and another instance is in need of the same block, it is easy to get the block image from the instance which has the block in its SGA rather than reading from the disk. To enable inter instance communication Oracle RAC makes use of interconnects. The Global Enqueue Service (GES) monitors and Instance enqueue process manages the cache fusion.

What command would you use to check the availability of the RAC system? crs_stat -t -v (-t -v are optional)

How do we verify that RAC instances are running?
SQL>select * from V$ACTIVE_INSTANCES;
The query gives the instance number under INST_NUMBER column,host_:instancename under INST_NAME column.

How can you connect to a specific node in a RAC environment? tnsnames.ora ensure that you have INSTANCE_NAME specified in it.

Which is the "MASTER NODE" in RAC?
The node with the lowest node number will become master node and dynamic remastering of the resources will take place.
To find out the master node for particular resource, you can query v$ges_resource for MASTER_NODE column.
To find out which is the master node, you can see ocssd.log file and search for "master node number". when the first master node fails in the cluster the lowest node number will become master node.

What components in RAC must reside in shared storage?
All datafiles, controlfiles, SPFIles, redo log files must reside on cluster-aware shred storage.

Give few examples for solutions that support cluster storage?
·ASM (automatic storage management),
·Raw disk devices,
·Network file system (NFS),
·OCFS2 and
·OCFS (Oracle Cluster Fie systems).

What are Oracle Cluster Components?
1.Cluster Interconnect (HAIP)
2.Shared Storage (OCR/Voting Disk)
3.Clusterware software
4.Oracle Kernel Components

What are Oracle RAC Components?
VIP, Node apps etc.

What are Oracle Kernel Components?
Basically Oracle kernel need to switched on with RAC On option when you convert to RAC, that is the difference as it facilitates few RAC bg process like LMON,LCK,LMD,LMS etc.

How to turn on RAC?
# link the oracle libraries
$ cd $ORACLE_HOME/rdbms/lib
$ make -f ins_rdbms.mk rac_on
# rebuild oracle
$ cd $ORACLE_HOME/bin
$ relink oracle

Disk architecture in RAC?
SAN (Storage Area Networks) - generally using fiber to connect to the SAN
NAS (Network Attached Storage) - generally using a network to connect to the NAS using either NFS, ISCSI

What is Oracle Clusterware?
The Clusterware software allows nodes to communicate with each other and forms the cluster that makes the nodes work as a single logical server.
The software is run by the Cluster Ready Services (CRS) using the Oracle Cluster Registry (OCR) that records and maintains the cluster and node membership information and the voting disk which acts as a tiebreaker during communication failures. Consistent heartbeat information travels across the interconnect to the voting disk when the cluster is running.

Real Application Clusters
Oracle RAC is a cluster database with a shared cache architecture that overcomes the limitations of traditional shared-nothing and shared-disk approaches to provide a highly scalable and available database solution for all your business applications. Oracle RAC provides the foundation for enterprise grid computing.

Oracle’s Real Application Clusters (RAC) option supports the transparent deployment of a single database across a cluster of servers, providing fault tolerance from hardware failures or planned outages. Oracle RAC running on clusters provides Oracle’s highest level of capability in terms of availability, scalability, and low-cost computing.

One DB opened by multipe instances so the the db ll be Highly Available if an instance crashes.
Cluster Software. Oracles Clusterware or products like Veritas Volume Manager are required to provide the cluster support and allow each node to know which nodes belong to the cluster and are available and with Oracle Cluterware to know which nodes have failed and to eject then from the cluster, so that errors on that node can be cleared.

Oracle Clusterware has two key components Cluster Registry OCR and Voting Disk.

The cluster registry holds all information about nodes, instances, services and ASM storage if used, it also contains state information ie they are available and up or similar.

The voting disk is used to determine if a node has failed, i.e. become separated from the majority. If a node is deemed to no longer belong to the majority then it is forcibly rebooted and will after the reboot add itself again the the surviving cluster nodes.

What are the Oracle Clusterware key components?
Oracle Clusterware has two key components Cluster Registry OCR and Voting Disk.

What is Voting Disk and OCR?
Voting Disk
Oracle RAC uses the voting disk to manage cluster membership by way of a health check and arbitrates cluster ownership among the instances in case of network failures. The voting disk must reside on shared disk.
A node must be able to access more than half of the voting disks at any time.
For example, if you have 3 voting disks configured, then a node must be able to access at least two of the voting disks at any time. If a node cannot access the minimum required number of voting disks it is evicted, or removed, from the cluster.

Oracle Cluster Registry (OCR)
The cluster registry holds all information about nodes, instances, services and ASM storage if used, it also contains state information ie they are available and up or similar.
The OCR must reside on shared disk that is accessible by all of the nodes in your cluster.

What are the administrative tasks involved with voting disk?
Following administrative tasks are performed with the voting disk :
1) Backing up voting disks
2) Recovering Voting disks
3) Adding voting disks
4) Deleting voting disks
5) Moving voting disks

Can you add voting disk online? Do you need voting disk backup?
Yes, as per documentation, if you have multiple voting disk you can add online, but if you have only one voting disk , by that cluster will be down as its lost you just need to start crs in exclusive mode and add the votedisk using crsctl add votedisk <path>

What is the Oracle Recommendation for backing up voting disk?
Oracle recommends us to use the dd command to backup the voting disk with a minimum block size of 4KB.

How do we backup voting disks?
1) Oracle recommends that you back up your voting disk after the initial cluster creation and after we complete any node addition or deletion procedures.
2) First, as root user, stop Oracle Clusterware (with the crsctl stop crs command) on all nodes. Then, determine the current voting disk by issuing the following command: crsctl query votedisk css
3) Then, issue the dd or ocopy command to back up a voting disk, as appropriate.
Give the syntax of backing up voting disks:-
On Linux or UNIX systems: dd if=voting_disk_name of=backup_file_name where, voting_disk_name is the name of the active voting disk backup_file_name is the name of the file to which we want to back up the voting disk contents
On Windows systems, use the ocopy command: copy voting_disk_name backup_file_name

How do we verify an existing current backup of OCR?
We can verify the current backup of OCR using the following command : ocrconfig -showbackup

You have lost OCR disk, what is your next step?
The cluster stack will be down due to the fact that cssd is unable to maintain the integrity, this is true in 10g, From 11gR2 onwards, the crsd stack will be down, the hasd still up and running. You can add the ocr back by restoring the automatic backup or import the manual backup,

What are the major RAC wait events?
In a RAC environment the buffer cache is global across all instances in the cluster and hence the processing differs. The most common wait events related to this are gc cr request and gc buffer busy

GC CR request :the time it takes to retrieve the data from the remote cache
Reason: RAC Traffic Using Slow Connection or Inefficient queries (poorly tuned queries will increase the amount of data blocks requested by an Oracle session. The more blocks requested typically means the more often a block will need to be read from a remote instance via the interconnect.)

GC BUFFER BUSY: It is the time the remote instance locally spends accessing the requested data block.

What do you do if you see GC CR BLOCK LOST in top 5 Timed Events in AWR Report?
This is most likely due to a fault in interconnect network.
Check netstat -s if you see "fragments dropped" or "packet reassemblies failed" , Work with your system administrator find the fault with network.

How do you troubleshoot node reboot?
Please check metalink ...
Note 265769.1 Troubleshooting CRS Reboots
Note.559365.1 Using Diagwait as a diagnostic to get more information for diagnosing Oracle Clusterware Node evictions.

Srvctl cannot start instance, I get the following error PRKP-1001 CRS-0215, however sqlplus can start it on both nodes? How do you identify the problem?
Set the environmental variable SRVM_TRACE to true.. And start the instance with srvctl. Now you will get detailed error stack.

What are Oracle Clusterware processes for 10g on Unix and Linux?
Cluster Synchronization Services (ocssd) — Manages cluster node membership and runs as the oracle user; failure of this process results in cluster restart.

Cluster Ready Services (crsd) — The crs process manages cluster resources (which could be a database, an instance, a service, a Listener, a virtual IP (VIP) address, an application process, and so on) based on the resource's configuration information that is stored in the OCR. This includes start, stop, monitor and failover operations. This process runs as the root user

Event manager daemon (evmd) —A background process that publishes events that crs creates.

Process Monitor Daemon (OPROCD) —This process monitor the cluster and provide I/O fencing. OPROCD performs its check, stops running, and if the wake up is beyond the expected time, then OPROCD resets the processor and reboots the node. An OPROCD failure results in Oracle Clusterware restarting the node. OPROCD uses the hangcheck timer on Linux platforms.

RACG (racgmain, racgimon) —Extends clusterware to support Oracle-specific requirements and complex resources. Runs server callout scripts when FAN events occur.

What are Oracle database background processes specific to RAC?
Oracle RAC is composed of two or more database instances. They are composed of Memory structures and background processes same as the single instance database.Oracle RAC instances use two processes GES(Global Enqueue Service), GCS(Global Cache Service) that enable cache fusion.Oracle RAC instances are composed of following background processes:
ACMS—Atomic Controlfile to Memory Service (ACMS)
GTX0-j—Global Transaction Process
LMON—Global Enqueue Service Monitor
LMD—Global Enqueue Service Daemon
LMS—Global Cache Service Process
LCK0—Instance Enqueue Process
RMSn—Oracle RAC Management Processes (RMSn)
RSMN—Remote Slave Monitor
To ensure that each Oracle RAC database instance obtains the block that it needs to satisfy a query or transaction, Oracle RAC instances use two processes, the Global Cache Service (GCS) and the Global Enqueue Service (GES). The GCS and GES maintain records of the statuses of each data file and each cached block using a Global Resource Directory (GRD). The GRD contents are distributed across all of the active instances.

What is GRD?
GRD stands for Global Resource Directory. The GES and GCS maintains records of the statuses of each datafile and each cahed block using global resource directory.This process is referred to as cache fusion and helps in data integrity.

What is ACMS?
ACMS stands for Atomic Controlfile Memory Service.In an Oracle RAC environment ACMS is an agent that ensures a distributed SGA memory update (ie)SGA updates are globally committed on success or globally aborted in event of a failure.

What is SCAN listener?
A scan listener is something that additional to node listener which listens the incoming db connection requests from the client which got through the scan IP, it got end points configured to node listener where it routes the db connection requests to particular node listener.

SCAN IP can be disabled if not required. However SCAN IP is mandatory during the RAC installation. Enabling/disabling SCAN IP is mostly used in oracle apps environment by the concurrent manager (kind of job scheduler in oracle apps).
Steps to disable the SCAN IP,
i. Do not use SCAN IP at the client end. ii. Stop scan listener srvctl stop scan_listener iii.Stop scan srvctl stop scan (this will stop the scan vip's) iv. Disable scan and disable scan listener srvctl disable scan

What are the different network components are in 10g RAC? public, private, and vip components
Private interfaces is for intra node communication.
VIP is all about availability of application. When a node fails then the VIP component fail over to some other node, this is the reason that all applications should based on vip components means tns entries should have vip entry in the host list

What is an interconnect network?
An interconnect network is a private network that connects all of the servers in a cluster. The interconnect network uses a switch/multiple switches that only the nodes in the cluster can access.

What is the use of cluster interconnect?
Cluster interconnect is used by the Cache fusion for inter instance communication.

How can we configure the cluster interconnect?
· Configure User Datagram Protocol (UDP) on Gigabit Ethernet for cluster interconnects.
· On UNIX and Linux systems we use UDP and RDS (Reliable data socket) protocols to be used by Oracle Clusterware.
· Windows clusters use the TCP protocol.

What is the purpose of Private Interconnect?
Clusterware uses the private interconnect for cluster synchronization (network heartbeat) and daemon communication between the the clustered nodes. This communication is based on the TCP protocol.
RAC uses the interconnect for cache fusion (UDP) and inter-process communication (TCP). Cache Fusion is the remote memory mapping of Oracle buffers, shared between the caches of participating nodes in the cluster.

What is a virtual IP address or VIP?
A virtual IP address or VIP is an alternate IP address that the client connections use instead of the standard public IP address. To configure VIP address, we need to reserve a spare IP address for each node, and the IP addresses must use the same subnet as the public network.

What is the use of VIP?
If a node fails, then the node's VIP address fails over to another node on which the VIP address can accept TCP connections but it cannot accept Oracle connections.

Why do we have a Virtual IP (VIP) in Oracle RAC?
Without using VIPs or FAN, clients connected to a node that died will often wait for a TCP timeout period (which can be up to 10 min) before getting an error. As a result, you don't really have a good HA solution without using VIPs.
When a node fails, the VIP associated with it is automatically failed over to some other node and new node re-arps the world indicating a new MAC address for the IP. Subsequent packets sent to the VIP go to the new node, which will send error RST packets back to the clients. This results in the clients getting errors immediately.

Give situations under which VIP address failover happens?
VIP addresses failover happens when the node on which the VIP address runs fails; all interfaces for the VIP address fails, all interfaces for the VIP address are disconnected from the network.

What is the significance of VIP address failover?
When a VIP address failover happens, Clients that attempt to connect to the VIP address receive a rapid connection refused error .They don't have to wait for TCP connection timeout messages.

What is the use of a service in Oracle RAC environment?
Applications should use the services feature to connect to the Oracle database. Services enable us to define rules and characteristics to control how users and applications connect to database instances.

What are the characteristics controlled by Oracle services feature?
The characteristics include a unique name, workload balancing, failover options, and high availability.

What enables the load balancing of applications in RAC?
Oracle Net Services enable the load balancing of application connections across all of the instances in an Oracle RAC database.

What are the types of connection load-balancing?
Connection Workload management is one of the key aspects when you have RAC instances as you want to distribute the connections to specific nodes/instance or those have less load.
There are two types of connection load-balancing:
1.Client Side load balancing (also called as connect time load balancing)
2.Server side load balancing (also called as Listener connection load balancing)

What is the difference between server-side and client-side connection load balancing?
Client-side balancing happens at client side where load balancing is done using listener.In case of server-side load balancing listener uses a load-balancing advisory to redirect connections to the instance providing best service.

Client Side load balancing:- Oracle client side load balancing feature enables clients to randomize the connection requests among all the available listeners based on their load.

An tns entry that contains all nodes entries and use load_balance=on (default its on) will use the connect time load balancing or client side load balancing.

Sample Client Side TNS Entry:-

finance = (DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = myrac2-vip)(PORT = 2042)) (ADDRESS = (PROTOCOL = TCP)(HOST = myrac1-vip)(PORT = 2042)) (ADDRESS = (PROTOCOL = TCP)(HOST = myrac3-vip)(PORT = 2042)) (LOAD_BALANCE = yes) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = FINANCE) (FAILOVER=ON) (FAILOVER_MODE = (TYPE = SELECT) (METHOD = BASIC) (RETRIES = 180) (DELAY = 5)) ) )

Server side load balancing:- This improves the connection performance by balancing the number of active connections among multiple instances and dispatchers. In a single instance environment (shared servers), the listener selects the least dispatcher to handle the incoming client requests. In a rac environments, PMON is aware of all instances load and dispatchers , and depending on the load information PMON redirects the connection to the least loaded node.

In a RAC environment, *.remote_listener parameter which is a tns entry containing all nodes addresses need to set to enable the load balance advisory updates to PMON.

Sample Tns entry should be in an instances of RAC cluster,

local_listener=LISTENER_MYRAC1 remote_listener = LISTENERS_MYRACDB

What are the administrative tools used for Oracle RAC environments?
Oracle RAC cluster can be administered as a single image using the below
· OEM (Enterprise Manager),
· SQL*PLUS,
· Server control (SRVCTL),
· Cluster Verification Utility (CLUVFY),
· DBCA,
· NETCA

Name some Oracle Clusterware tools and their uses?
·OIFCFG - allocating and deallocating network interfaces.
·OCRCONFIG - Command-line tool for managing Oracle Cluster Registry.
·OCRDUMP - Identify the interconnect being used.
·CVU - Cluster verification utility to get status of CRS resources.

What is the difference between CRSCTL and SRVCTL? crsctl manages clusterware-related operations: Starting and stopping Oracle Clusterware Enabling and disabling Oracle Clusterware daemons Registering cluster resources

srvctl manages Oracle resource–related operations: Starting and stopping database instances and services Also from 11gR2 manages the cluster resources like network,vip,disks etc

How do we remove ASM from a Oracle RAC environment?
We need to stop and delete the instance in the node first in interactive or silent mode.After that asm can be removed using srvctl tool as follows: srvctl stop asm -n node_name srvctl remove asm -n node_name
We can verify if ASM has been removed by issuing the following command: srvctl config asm -n node_name

How do we verify that an instance has been removed from OCR after deleting an instance?
Issue the following srvctl command: srvctl config database -d database_name cd CRS_HOME/bin
./crs_stat

What are the modes of deleting instances from ORacle Real Application cluster Databases?
We can delete instances using silent mode or interactive mode using DBCA(Database Configuration Assistant).

What are the background process that exists in 11gr2 and functionality?
Process Name Functionality crsd •The CRS daemon (crsd) manages cluster resources based on configuration information that is stored in Oracle Cluster Registry (OCR) for each resource. This includes start, stop, monitor, and failover operations. The crsd process generates events when the status of a resource changes. cssd •Cluster Synchronization Service (CSS): Manages the cluster configuration by controlling which nodes are members of the cluster and by notifying members when a node joins or leaves the cluster. If you are using certified third-party clusterware, then CSS processes interfaces with your clusterware to manage node membership information. CSS has three separate processes: the CSS daemon (ocssd), the CSS Agent (cssdagent), and the CSS Monitor (cssdmonitor). The cssdagent process monitors the cluster and provides input/output fencing. This service formerly was provided by Oracle Process Monitor daemon (oprocd), also known as OraFenceService on Windows. A cssdagent failure results in Oracle Clusterware restarting the node. diskmon •Disk Monitor daemon (diskmon): Monitors and performs input/output fencing for Oracle Exadata Storage Server. As Exadata storage can be added to any Oracle RAC node at any point in time, the diskmon daemon is always started when ocssd is started. evmd •Event Manager (EVM): Is a background process that publishes Oracle Clusterware events mdnsd •Multicast domain name service (mDNS): Allows DNS requests. The mDNS process is a background process on Linux and UNIX, and a service on Windows. gnsd •Oracle Grid Naming Service (GNS): Is a gateway between the cluster mDNS and external DNS servers. The GNS process performs name resolution within the cluster. ons •Oracle Notification Service (ONS): Is a publish-and-subscribe service for communicating Fast Application Notification (FAN) events oraagent •oraagent: Extends clusterware to support Oracle-specific requirements and complex resources. It runs server callout scripts when FAN events occur. This process was known as RACG in Oracle Clusterware 11g Release 1 (11.1). orarootagent •Oracle root agent (orarootagent): Is a specialized oraagent process that helps CRSD manage resources owned by root, such as the network, and the Grid virtual IP address oclskd •Cluster kill daemon (oclskd): Handles instance/node evictions requests that have been escalated to CSS gipcd •Grid IPC daemon (gipcd): Is a helper daemon for the communications infrastructure ctssd •Cluster time synchronisation daemon(ctssd) to manage the time syncrhonization between nodes, rather depending on NTP

Under which user or owner the process will start?
Component Name of the Process Owner
Oracle High Availability Service ohasd init, root
Cluster Ready Service (CRS) Cluster Ready Services root
Cluster Synchronization Service (CSS) ocssd,cssd monitor, cssdagent grid owner
Event Manager (EVM) evmd, evmlogger grid owner
Cluster Time Synchronization Service (CTSS) octssd root
Oracle Notification Service (ONS) ons, eons grid owner
Oracle Agent oragent grid owner
Oracle Root Agent orarootagent root
Grid Naming Service (GNS) gnsd root
Grid Plug and Play (GPnP) gpnpd grid owner
Multicast domain name service (mDNS) mdnsd grid owner

What is the major difference between 10g and 11g RAC?
There is not much difference between 10g and 11gR (1) RAC. But there is a significant difference in 11gR2.

Prior to 11gR1(10g) RAC, the following were managed by Oracle CRS Databases Instances Applications Node Monitoring Event Services High Availability

From 11gR2(onwards) its completed HA stack managing and providing the following resources as like the other cluster software like VCS etc. Databases Instances Applications Cluster Management Node Management Event Services High Availability Network Management (provides DNS/GNS/MDNSD services on behalf of other traditional services) and SCAN – Single Access Client Naming method, HAIP Storage Management (with help of ASM and other new ACFS filesystem) Time synchronization (rather depending upon traditional NTP) Removed OS dependent hang checker etc, manages with own additional monitor process

What is hangcheck timer?
The hangcheck timer checks regularly the health of the system. If the system hangs or stop the node will be restarted automatically.
There are 2 key parameters for this module:
-> hangcheck-tick: this parameter defines the period of time between checks of system health. The default value is 60 seconds; Oracle recommends setting it to 30seconds.
-> hangcheck-margin: this defines the maximum hang delay that should be tolerated before hangcheck-timer resets the RAC node.

State the initialization parameters that must have same value for every instance in an Oracle RAC database?
Some initialization parameters are critical at the database creation time and must have same values.Their value must be specified in SPFILE or PFILE for every instance.The list of parameters that must be identical on every instance are given below:
ACTIVE_INSTANCE_COUNT
ARCHIVE_LAG_TARGET
COMPATIBLE
CLUSTER_DATABASE
CLUSTER_DATABASE_INSTANCE
CONTROL_FILES
DB_BLOCK_SIZE
DB_DOMAIN
DB_FILES
DB_NAME
DB_RECOVERY_FILE_DEST
DB_RECOVERY_FILE_DEST_SIZE
DB_UNIQUE_NAME
INSTANCE_TYPE (RDBMS or ASM)
PARALLEL_MAX_SERVERS
REMOTE_LOGIN_passWORD_FILE
UNDO_MANAGEMENT

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What is RAC? What is the benefit of RAC over single instance database?
In Real Application Clusters environments, all nodes concurrently execute transactions against the same database. Real Application Clusters coordinates each node's access to the shared data to provide consistency and integrity.
Benefits:
Improve response time
Improve throughput
High availability
Transparency

Advantages of RAC (Real Application Clusters)

Reliability - if one node fails, the database won't fail
Availability - nodes can be added or replaced without having to shutdown the database
Scalability - more nodes can be added to the cluster as the workload increases

What is a virtual IP address or VIP?

A virtual IP address or VIP is an alternate IP address that the client connections use instead of the standard public IP address. To configure VIP address, we need to reserve a spare IP address for each node, and the IP addresses must use the same subnet as the public network.

What is the use of VIP?
If a node fails, then the node's VIP address fails over to another node on which the VIP address can accept TCP connections but it cannot accept Oracle connections.
Give situations under which VIP address failover happens:-
VIP addresses failover happens when the node on which the VIP address runs fails, all interfaces for the VIP address fails, all interfaces for the VIP address are disconnected from the network.
Using virtual IP we can save our TCP/IP timeout problem because Oracle notification service maintains communication between each nodes and listeners.

What is the significance of VIP address failover?
When a VIP address failover happens, Clients that attempt to connect to the VIP address receive a rapid connection refused error .They don't have to wait for TCP connection timeout messages.

What is voting disk?
Voting Disk is a file that sits in the shared storage area and must be accessible by all nodes in the cluster. All nodes in the cluster registers their heart-beat information in the voting disk, so as to confirm that they are all operational. If heart-beat information of any node in the voting disk is not available that node will be evicted from the cluster. The CSS (Cluster Synchronization Service) daemon in the clusterware maintains the heart beat of all nodes to the voting disk. When any node is not able to send heartbeat to voting disk, then it will reboot itself, thus help avoiding the split-brain syndrome.

For high availability, Oracle recommends that you have a minimum of three or odd number (3 or greater) of votingdisks.

Voting Disk - is file that resides on shared storage and Manages cluster members. Voting disk reassigns cluster ownership between the nodes in case of failure.

The Voting Disk Files are used by Oracle Clusterware to determine which nodes are currently members of the cluster. The voting disk files are also used in concert with other Cluster components such as CRS to maintain the clusters integrity.

Oracle Database 11g Release 2 provides the ability to store the voting disks in ASM along with the OCR. Oracle Clusterware can access the OCR and the voting disks present in ASM even if the ASM instance is down. As a result CSS can continue to maintain the Oracle cluster even if the ASM instance has failed.

How many voting disks are you maintaining ?

http://www.toadworld.com/KNOWLEDGE/KnowledgeXpertforOracle/tabid/648/TopicID/RACR2ARC6/Default.aspx

By default Oracle will create 3 voting disk files in ASM.

Oracle expects that you will configure at least 3 voting disks for redundancy purposes. You should always configure an odd number of voting disks >= 3. This is because loss of more than half your voting disks will cause the entire cluster to fail.

You should plan on allocating 280MB for each voting disk file. For example, if you are using ASM and external redundancy then you will need to allocate 280MB of disk for the voting disk. If you are using ASM and normal redundancy you will need 560MB.

Why we need to keep odd number of voting disks ?
Oracle expects that you will configure at least 3 voting disks for redundancy purposes. You should always configure an odd number of voting disks >= 3. This is because loss of more than half your voting disks will cause the entire cluster to fail.

What are Oracle RAC software components?
Oracle RAC is composed of two or more database instances. They are composed of Memory structures and background processes same as the single instance database.Oracle RAC instances use two processes GES(Global Enqueue Service), GCS(Global Cache Service) that enable cache fusion.Oracle RAC instances are composed of following background processes:
ACMS—Atomic Controlfile to Memory Service (ACMS)
GTX0-j—Global Transaction Process
LMON—Global Enqueue Service Monitor
LMD—Global Enqueue Service Daemon
LMS—Global Cache Service Process
LCK0—Instance Enqueue Process
RMSn—Oracle RAC Management Processes (RMSn)
RSMN—Remote Slave Monitor

What are Oracle Clusterware processes for 10g ?
Cluster Synchronization Services (ocssd) — Manages cluster node membership and runs as the oracle user; failure of this process results in cluster restart.
Cluster Ready Services (crsd) — The crs process manages cluster resources (which could be a database, an instance, a service, a Listener, a virtual IP (VIP) address, an application process, and so on) based on the resource's configuration information that is stored in the OCR. This includes start, stop, monitor and failover operations. This process runs as the root user
Event manager daemon (evmd) —A background process that publishes events that crs creates.
Process Monitor Daemon (OPROCD) —This process monitor the cluster and provide I/O fencing. OPROCD performs its check, stops running, and if the wake up is beyond the expected time, then OPROCD resets the processor and reboots the node. An OPROCD failure results in Oracle Clusterware restarting the node. OPROCD uses the hangcheck timer on Linux platforms.
RACG (racgmain, racgimon) —Extends clusterware to support Oracle-specific requirements and complex resources. Runs server callout scripts when FAN events occur.

What are Oracle database background processes specific to RAC?
LMS—Global Cache Service Process
LMD—Global Enqueue Service Daemon
LMON—Global Enqueue Service Monitor
LCK0—Instance Enqueue Process
Oracle RAC instances use two processes, the Global Cache Service (GCS) and the Global Enqueue Service (GES). The GCS and GES maintain records of the statuses of each data file and each cached block using a Global Resource Directory (GRD). The GRD contents are distributed across all of the active instances.

What is Cache Fusion?
Transfor of data across instances through private interconnect is called cachefusion.Oracle RAC is composed of two or more instances. When a block of data is read from datafile by an instance within the cluster and another instance is in need of the same block,it is easy to get the block image from the insatnce which has the block in its SGA rather than reading from the disk. To enable inter instance communication Oracle RAC makes use of interconnects. The Global Enqueue Service(GES) monitors and Instance enqueue process manages the cahce fusion

What is SCAN? (11gR2 feature)
Single Client Access Name (SCAN) is s a new Oracle Real Application Clusters (RAC) 11g Release 2 feature that provides a single name for clients to access an Oracle Database running in a cluster. The benefit is clients using SCAN do not need to change if you add or remove nodes in the cluster.

SCAN provides a single domain name via (DNS), allowing and-users to address a RAC cluster as-if it were a single IP address. SCAN works by replacing a hostname or IP list with virtual IP addresses (VIP).

Single client access name (SCAN) is meant to facilitate single name for all Oracle clients to connect to the cluster database, irrespective of number of nodes and node location. Until now, we have to keep adding multiple address records in all clients tnsnames.ora, when a new node gets added to or deleted from the cluster.

Single Client Access Name (SCAN) eliminates the need to change TNSNAMES entry when nodes are added to or removed from the Cluster. RAC instances register to SCAN listeners as remote listeners. Oracle recommends assigning 3 addresses to SCAN, which will create 3 SCAN listeners, though the cluster has got dozens of nodes.. SCAN is a domain name registered to at least one and up to three IP addresses, either in DNS (Domain Name Service) or GNS (Grid Naming Service). The SCAN must resolve to at least one address on the public network. For high availability and scalability, Oracle recommends configuring the SCAN to resolve to three addresses. http://www.freeoraclehelp.com/2011/12/scan-setup-for-oracle-11g-release211gr2.html What are SCAN components in a cluster?
1.SCAN Name
2.SCAN IPs (3)
3.SCAN Listeners (3)
What is FAN?
Fast application Notification as it abbreviates to FAN relates to the events related to instances,services and nodes.This is a notification mechanism that Oracle RAc uses to notify other processes about the configuration and service level information that includes service status changes such as,UP or DOWN events.Applications can respond to FAN events and take immediate action.

What is TAF?
TAF (Transparent Application Failover) is a configuration that allows session fail-over between different nodes of a RAC database cluster.
Transparent Application Failover (TAF). If a communication link failure occurs after a connection is established, the connection fails over to another active node. Any disrupted transactions are rolled back, and session properties and server-side program variables are lost. In some cases, if the statement executing at the time of the failover is a Select statement, that statement may be automatically re-executed on the new connection with the cursor positioned on the row on which it was positioned prior to the failover.

After an Oracle RAC node crashes—usually from a hardware failure—all new application transactions are automatically rerouted to a specified backup node. The challenge in rerouting is to not lose transactions that were "in flight" at the exact moment of the crash. One of the requirements of continuous availability is the ability to restart in-flight application transactions, allowing a failed node to resume processing on another server without interruption. Oracle's answer to application failover is a new Oracle Net mechanism dubbed Transparent Application Failover. TAF allows the DBA to configure the type and method of failover for each Oracle Net client.
TAF architecture offers the ability to restart transactions at either the transaction (SELECT) or session level.
What are the requirements for Oracle Clusterware?
1. External Shared Disk to store Oracle Cluster ware file (Voting Disk and Oracle Cluster Registry - OCR)
2. Two netwrok cards on each cluster ware node (and three set of IP address) -
Network Card 1 (with IP address set 1) for public network
Network Card 2 (with IP address set 2) for private network (for inter node communication between rac nodes used by clusterware and rac database)
IP address set 3 for Virtual IP (VIP) (used as Virtual IP address for client connection and for connection failover)
3. Storage Option for OCR and Voting Disk - RAW, OCFS2 (Oracle Cluster File System), NFS, …..
Which enable the load balancing of applications in RAC?
Oracle Net Services enable the load balancing of application connections across all of the instances in an Oracle RAC database.

How to find location of OCR file when CRS is down?
If you need to find the location of OCR (Oracle Cluster Registry) but your CRS is down.
When the CRS is down:
Look into “ocr.loc” file, location of this file changes depending on the OS:
On Linux: /etc/oracle/ocr.loc
On Solaris: /var/opt/oracle/ocr.loc
When CRS is UP:
Set ASM environment or CRS environment then run the below command: ocrcheck In 2 node RAC, how many NIC’s are r using ?
2 network cards on each clusterware node
Network Card 1 (with IP address set 1) for public network
Network Card 2 (with IP address set 2) for private network (for inter node communication between rac nodes used by clusterware and rac database)

In 2 node RAC, how many IP’s are r using ?
6 - 3 set of IP address
## eth1-Public: 2
## eth0-Private: 2
## VIP: 2

How to find IP’s information in RAC ?
Edit the /etc/hosts file as shown below:
# Do not remove the following line, or various programs
# that requires network functionality will fail.
127.0.0.1 localhost.localdomain localhost
## Public Node names 192.168.10.11 node1-pub.hingu.net node1-pub
192.168.10.22 node2-pub.hingu.net node2-pub
## Private Network (Interconnect) 192.168.0.11 node1-prv node1-prv
192.168.0.22 node2-prv node2-prv
## Private Network (Network Area storage) 192.168.1.11 node1-nas node1-nas
192.168.1.22 node2-nas node2-nas
192.168.1.33 nas-server nas-server
## Virtual IPs 192.168.10.111 node1-vip.hingu.net node1-vip
192.168.10.222 node2-vip.hingu.net node2-vip

What is difference between RAC ip addresses ?
Public IP adress is the normal IP address typically used by DBA and SA to manage storage, system and database. Public IP addresses are reserved for the Internet.
Private IP address is used only for internal clustering processing (Cache Fusion) (aka as interconnect). Private IP addresses are reserved for private networks.
VIP is used by database applications to enable fail over when one cluster node fails. The purpose for having VIP is so client connection can be failover to surviving nodes in case there is failure

Can application developer access the private ip ?
No. private IP address is used only for internal clustering processing (Cache Fusion) (aka as interconnect) http://rajeevjhaoracle.wordpress.com/2012/01/02/oracle-rac-interview-question-answer/ What is RAC?

RAC Architechture?

What is a SCAN Listener?

What is VIP?

What is TAF?

What is FAN?

What is LMON?

What is CACHE FUSION?

What is SPLIT BRAIN in RAC?

How Load balancing works in ORACLE RAC?

What is Voting Disk?
How many backups are there for Voting Disk?

WHY ODD NUMBER OF VOTING DISK IS USED?
How to take Voting Disk backup? Do you take Voting Disk backup?
If you lost Voting Disk, how do you Restore?

What is OCR?
How many backups are there for OCR?
How to take OCR backup? Do you take OCR backup?
If you lost OCR, how do you Restore?

What is a Master Node?
How do you know which is the Master Node without connecting to Database?

Can we have Node 1 in SOLARIS OS and Node 2 in LINUX OS?

Commonly used commands in RAC?

How to convert standalone database to RAC?
1. Where are the Clusterware files stored on a RAC environment?
The Clusterware is installed on each node (on an Oracle Home) and on the shared disks (the voting disks and the CSR file)
2. Where are the database software files stored on a RAC environment?
The base software is installed on each node of the cluster and the database storage on the shared disks.
3. What kind of storage we can use for the shared Clusterware files?
- OCFS (Release 1 or 2)
- raw devices
- third party cluster file system such as GPFS or Veritas
4. What kind of storage we can use for the RAC database storage?
- OCFS (Release 1 or 2)
- ASM
- raw devices
- third party cluster file system such as GPFS or Veritas
5. What is a CFS?
A cluster File System (CFS) is a file system that may be accessed (read and write) by all members in a cluster at the same time. This implies that all members of a cluster have the same view.
6. What is an OCFS2?
The OCFS2 is the Oracle (version 2) Cluster File System which can be used for the Oracle Real Application Cluster.
7. Which files can be placed on an Oracle Cluster File System?
- Oracle Software installation (Windows only)
- Oracle files (controlfiles, datafiles, redologs, files described by the bfile datatype)
- Shared configuration files (spfile)
- OCR and voting disk
- Files created by Oracle during runtime
Note: There are some platform specific limitations.
8. Do you know another Cluster Vendor?
HP Tru64 Unix, Veritas, Microsoft
9. How is possible to install a RAC if we don’t have a CFS?
This is possible by using a raw device.
10. What is a raw device?
A raw device is a disk drive that does not yet have a file system set up. Raw devices are used for Real Application Clusters since they enable the sharing of disks.
11. What is a raw partition?
A raw partition is a portion of a physical disk that is accessed at the lowest possible level. A raw partition is created when an extended partition is created and logical partitions are assigned to it without any formatting. Once formatting is complete, it is called cooked partition.
12. When to use CFS over raw?
A CFS offers:
- Simpler management
- Use of Oracle Managed Files with RAC
- Single Oracle Software installation
- Autoextend enabled on Oracle datafiles
- Uniform accessibility to archive logs in case of physical node failure
- With Oracle_Home on CFS, when you apply Oracle patches CFS guarantees that the updated Oracle_Home is visible to all nodes in the cluster.
Note: This option is very dependent on the availability of a CFS on your platform.
13. When to use raw over CFS?
- Always when CFS is not available or not supported by Oracle.
- The performance is very, very important: Raw devices offer best performance without any intermediate layer between Oracle and the disk.
Note: Autoextend fails on raw devices if the space is exhausted. However the space could be added online if needed.
14. What CRS is?
Oracle RAC 10g Release 1 introduced Oracle Cluster Ready Services (CRS), a platform-independent set of system services for cluster environments. In Release 2, Oracle has renamed this product to Oracle Clusterware.
15. What is VIP IP used for?
It returns a dead connection IMMIDIATELY, when its primary node fails. Without using VIP IP, the clients have to wait around 10 minutes to receive ORA-3113: “end of file on communications channel”. However, using Transparent Application Failover (TAF) could avoid ORA-3113.
16. Why we need to have configured SSH or RSH on the RAC nodes?
SSH (Secure Shell,10g+) or RSH (Remote Shell, 9i+) allows “oracle” UNIX account connecting to another RAC node and copy/ run commands as the local “oracle” UNIX account.
17. Is the SSH, RSH needed for normal RAC operations?
No. SSH or RSH are needed only for RAC, patch set installation and clustered database creation.
18. Do we have to have Oracle RDBMS on all nodes?
Each node of a cluster that is being used for a clustered database will typically have the RDBMS and RAC software loaded on it, but not actual data files (these need to be available via shared disk).
19. What are the restrictions on the SID with a RAC database? Is it limited to 5 characters?
The SID prefix in 10g Release 1 and prior versions was restricted to five characters by install/ config tools so that an ORACLE_SID of up to max of 5+3=8 characters can be supported in a RAC environment. The SID prefix is relaxed up to 8 characters in 10g Release 2, see bug 4024251 for more information.
20. Does Real Application Clusters support heterogeneous platforms?
The Real Application Clusters do not support heterogeneous platforms in the same cluster.

21. Are there any issues for the interconnect when sharing the same switch as the public network by using VLAN to separate the network?
RAC and Clusterware deployment best practices suggests that the interconnect (private connection) be deployed on a stand-alone, physically separate, dedicated switch. On big network the connections could be instable.
22. What is the Load Balancing Advisory?
To assist in the balancing of application workload across designated resources, Oracle Database 10g Release 2 provides the Load Balancing Advisory. This Advisory monitors the current workload activity across the cluster and for each instance where a service is active; it provides a percentage value of how much of the total workload should be sent to this instance as well as service quality flag.
23. How many nodes are supported in a RAC Database?
With 10g Release 2, we support 100 nodes in a cluster using Oracle Clusterware, and 100 instances in a RAC database. Currently DBCA has a bug where it will not go beyond 63 instances. There is also a documentation bug for the max-instances parameter. With 10g Release 1 the Maximum is 63.

24. What is the Cluster Verification Utiltiy (cluvfy)?
The Cluster Verification Utility (CVU) is a validation tool that you can use to check all the important components that need to be verified at different stages of deployment in a RAC environment.
25. What versions of the database can I use the cluster verification utility (cluvfy) with?
The cluster verification utility is release with Oracle Database 10g Release 2 but can also be used with Oracle Database 10g Release 1.
26. If I am using Vendor Clusterware such as Veritas, IBM, Sun or HP, do I still need Oracle Clusterware to run Oracle RAC 10g?
Yes. When certified, you can use Vendor Clusterware however you must still install and use Oracle Clusterware for RAC. Best Practice is to leave Oracle Clusterware to manage RAC. For details see Metalink Note 332257.1 and for Veritas SFRAC see 397460.1.
27. Is RAC on VMWare supported?
Yes.
28. What is hangcheck timer used for ?
The hangcheck timer checks regularly the health of the system. If the system hangs or stop the node will be restarted automatically.
There are 2 key parameters for this module:
-> hangcheck-tick: this parameter defines the period of time between checks of system health. The default value is 60 seconds; Oracle recommends setting it to 30seconds.
-> hangcheck-margin: this defines the maximum hang delay that should be tolerated before hangcheck-timer resets the RAC node.
29. Is the hangcheck timer still needed with Oracle RAC 10g?
Yes.
30. What files can I put on Linux OCFS2?
For optimal performance, you should only put the following files on Linux OCFS2:
- Datafiles
- Control Files
- Redo Logs
- Archive Logs
- Shared Configuration File (OCR)
- Voting File
- SPFILE
31. Is it possible to use ASM for the OCR and voting disk?
No, the OCR and voting disk must be on raw or CFS (cluster file system).
32. Can I change the name of my cluster after I have created it when I am using Oracle Clusterware?
No, you must properly uninstall Oracle Clusterware and then re-install.
33. What the O2CB is?
The O2CB is the OCFS2 cluster stack. OCFS2 includes some services. These services must be started before using OCFS2 (mount/ format the file systems).
34. What the OCR file is used for?
OCR is a file that manages the cluster and RAC configuration.
35. What the Voting Disk file is used for?
The voting disk is nothing but a file that contains and manages information of all the node memberships.
36. What is the recommended method to make backups of a RAC environment? RMAN to make backups of the database, dd to backup your voting disk and hard copies of the OCR file.
37. What command would you use to check the availability of the RAC system? crs_stat -t -v (-t -v are optional)
38. What is the minimum number of instances you need to have in order to create a RAC?
You can create a RAC with just one server.
39. Name two specific RAC background processes
RAC processes are: LMON, LMDx, LMSn, LKCx and DIAG.
40. Can you have many database versions in the same RAC?
Yes, but Clusterware version must be greater than the greater database version.
41. What was RAC previous name before it was called RAC?OPS: Oracle Parallel Server
42. What RAC component is used for communication between instances?Private Interconnect.
43. What is the difference between normal views and RAC views?A RAC view has the prefix ‘G’. For example, GV$SESSION instead of V$SESSION
44. Which command will we use to manage (stop, start) RAC services in command-line mode? srvctl 45. How many alert logs exist in a RAC environment?
A- One for each instance.
46. What are Oracle Clusterware Components
Voting Disk — Oracle RAC uses the voting disk to manage cluster membership by way of a health check and arbitrates cluster ownership among the instances in case of network failures. The voting disk must reside on shared disk.
Oracle Cluster Registry (OCR) — Maintains cluster configuration information as well as configuration information about any cluster database within the cluster. The OCR must reside on shared disk that is accessible by all of the nodes in your cluster
47. How do you backup voting disk
#dd if=voting_disk_name of=backup_file_name
48. How do I identify the voting disk location
#crsctl query css votedisk
49. How do I identify the OCR file location check /var/opt/oracle/ocr.loc or /etc/ocr.loc ( depends upon platform) or #ocrcheck
50. What is SCAN?
Single Client Access Name (SCAN) is s a new Oracle Real Application Clusters (RAC) 11g Release 2 feature that provides a single name for clients to access an Oracle Database running in a cluster. The benefit is clients using SCAN do not need to change if you add or remove nodes in the cluster.
1. What is the major difference between 10g and 11g RAC?
Well, there is not much difference between 10g and 11gR (1) RAC.
But there is a significant difference in 11gR2.
Prior to 11gR1(10g) RAC, the following were managed by Oracle CRS * Databases * Instances * Applications * Node Monitoring * Event Services * High Availability
From 11gR2(onwards) its completed HA stack managing and providing the following resources as like the other cluster software like VCS etc. * Databases * Instances * Applications * Cluster Management * Node Management * Event Services * High Availability * Network Management (provides DNS/GNS/MDNSD services on behalf of other traditional services) and SCAN – Single Access Client Naming method, HAIP * Storage Management (with help of ASM and other new ACFS filesystem) * Time synchronization (rather depending upon traditional NTP) * Removed OS dependent hang checker etc, manages with own additional monitor process
2. What are Oracle Cluster Components?
Cluster Interconnect (HAIP)
Shared Storage (OCR/Voting Disk)
Clusterware software
3. What are Oracle RAC Components?
VIP, Node apps etc.
4. What are Oracle Kernel Components (nothing but how does Oracle RAC database differs than Normal single instance database in terms of Binaries and process)
Basically Oracle kernel need to switched on with RAC On option when you convert to RAC, that is the difference as it facilitates few RAC bg process like LMON,LCK,LMD,LMS etc.
To turn on RAC
# link the oracle libraries
$ cd $ORACLE_HOME/rdbms/lib
$ make -f ins_rdbms.mk rac_on
# rebuild oracle
$ cd $ORACLE_HOME/bin
$ relink oracle
Oracle RAC is composed of two or more database instances. They are composed of Memory structures and background processes same as the single instance database.Oracle RAC instances use two processes GES(Global Enqueue Service), GCS(Global Cache Service) that enable cache fusion.Oracle RAC instances are composed of following background processes:
ACMS—Atomic Controlfile to Memory Service (ACMS)
GTX0-j—Global Transaction Process
LMON—Global Enqueue Service Monitor
LMD—Global Enqueue Service Daemon
LMS—Global Cache Service Process
LCK0—Instance Enqueue Process
RMSn—Oracle RAC Management Processes (RMSn)
RSMN—Remote Slave Monitor
5. What is Clusterware?
Software that provides various interfaces and services for a cluster. Typically, this includes capabilities that: * Allow the cluster to be managed as a whole * Protect the integrity of the cluster * Maintain a registry of resources across the cluster * Deal with changes to the cluster * Provide a common view of resources
6. What are the background process that exists in 11gr2 and functionality? Process Name | Functionality | crsd | •The CRS daemon (crsd) manages cluster resources based on configuration information that is stored in Oracle Cluster Registry (OCR) for each resource. This includes start, stop, monitor, and failover operations. The crsd process generates events when the status of a resource changes. | cssd | •Cluster Synchronization Service (CSS): Manages the cluster configuration by controlling which nodes are members of the cluster and by notifying members when a node joins or leaves the cluster. If you are using certified third-party clusterware, then CSS processes interfaces with your clusterware to manage node membership information. CSS has three separate processes: the CSS daemon (ocssd), the CSS Agent (cssdagent), and the CSS Monitor (cssdmonitor). The cssdagent process monitors the cluster and provides input/output fencing. This service formerly was provided by Oracle Process Monitor daemon (oprocd), also known as OraFenceService on Windows. A cssdagent failure results in Oracle Clusterware restarting the node. | diskmon | •Disk Monitor daemon (diskmon): Monitors and performs input/output fencing for Oracle Exadata Storage Server. As Exadata storage can be added to any Oracle RAC node at any point in time, the diskmon daemon is always started when ocssd is started. | evmd | •Event Manager (EVM): Is a background process that publishes Oracle Clusterware events | mdnsd | •Multicast domain name service (mDNS): Allows DNS requests. The mDNS process is a background process on Linux and UNIX, and a service on Windows. | gnsd | •Oracle Grid Naming Service (GNS): Is a gateway between the cluster mDNS and external DNS servers. The GNS process performs name resolution within the cluster. | ons | •Oracle Notification Service (ONS): Is a publish-and-subscribe service for communicating Fast Application Notification (FAN) events | oraagent | •oraagent: Extends clusterware to support Oracle-specific requirements and complex resources. It runs server callout scripts when FAN events occur. This process was known as RACG in Oracle Clusterware 11g Release 1 (11.1). | orarootagent | •Oracle root agent (orarootagent): Is a specialized oraagent process that helps CRSD manage resources owned by root, such as the network, and the Grid virtual IP address | oclskd | •Cluster kill daemon (oclskd): Handles instance/node evictions requests that have been escalated to CSS | gipcd | •Grid IPC daemon (gipcd): Is a helper daemon for the communications infrastructure | ctssd | •Cluster time synchronisation daemon(ctssd) to manage the time syncrhonization between nodes, rather depending on NTP |
7. Under which user or owner the process will start? Component | Name of the Process | Owner | Oracle High Availability Service | ohasd | init, root | Cluster Ready Service (CRS) | Cluster Ready Services | root | Cluster Synchronization Service (CSS) | ocssd,cssd monitor, cssdagent | grid owner | Event Manager (EVM) | evmd, evmlogger | grid owner | Cluster Time Synchronization Service (CTSS) | octssd | root | Oracle Notification Service (ONS) | ons, eons | grid owner | Oracle Agent | oragent | grid owner | Oracle Root Agent | orarootagent | root | Grid Naming Service (GNS) | gnsd | root | Grid Plug and Play (GPnP) | gpnpd | grid owner | Multicast domain name service (mDNS) | mdnsd | grid owner |
8. What is startup sequence in Oracle 11g RAC? 11g RAC startup sequence?
This is about to understand the startup sequence of Grid Infrastructure daemons and its resources in 11gR2 RAC. In 11g RAC aka Grid Infrastructure we all know there are additional background daemons and agents, and the Oracle documentation is not so clear nor the other blog. For example:- I have found below diagram from metalink which is very confusing.

Whilst reading the book “http://www.amazon.com/Pro-Oracle-Database-11g-Linux/dp/1430229586” found excellent diagram representing the same but very understandable manner. (at least for me)

Without much hassle or discussion with bottom to top approach, I understand now,
OHASD Phase:- * OHASD (Oracle High Availability Server Daemon) starts Firsts and it will start
OHASD Agent Phase:- * OHASD Agent starts and in turn this will start gipcd | Grid interprocess communication daemon, used for monitoring cluster interconnect | mdnsd | Multicast DNS service It resolves DNS requests on behalf of GNS | gns | The Grid Naming Service (GNS), a gateway between DNS and mdnsd, resolves DNS requests | gpnpd | Grid Plug and Play Daemon, Basically a profile similar like OCR contents stored in XML format in $GI_HOME/gpnp/profiles/<peer> etc., this is where used by OCSSD also to read the ASM disk locations to start up with out having ASM to be up, moreover this also provides the plug and play profile where this can be distributed across nodes to cluster | evmd/ evmlogger | Evm service will be provided by evmd daemon, which is a information about events happening in cluster, stop node,start node, start instance etc. | * cssdagent (cluster synchronization service agent), in turn starts ocssd | Cluster synchronization service daemon which manages node membership in the cluster |
If cssd found that ocssd is down, it will reboot the node to protect the data integrity. * cssdmonitor (cluster synchronization service monitor), replaces oprocd and provides I/O fencing * OHASD orarootagent starts and in turn starts crsd.bin | Cluster ready services, which manages high availability of cluster resources , like stopping , starting, failing over etc. | diskmon.bin | disk monitor (diskdaemon monitor) provides I/O fencing for exadata storage | octssd.bin | Cluster synchronization time services , provides Network time protocol services but manages its own rather depending on OS |
CRSD Agent Phase:- crsd.bin starts two more agents crsd orarootagent(Oracle root agent) starts and in turn this will start gns | Grid interprocess communication daemon, used for monitoring cluster interconnect | gns vip | Multicast DNS service It resolves DNS requests on behalf of GNS | Network | Monitor the additional networks to provide HAIP to cluster interconnects | Scan vip | Monitor the scan vip, if found fail or unreachable failed to other node | Node vip | Monitor the node vip, if found fail or unreachable failed to other node | crsd oraagent(Oracle Agent) starts and in turn it will start (the same functionality in 11gr1 and 10g managed by racgmain and racgimon background process) which is now managed by crs Oracle agent itself.
·
ASM & disk groups | Start & monitor local asm instance | ONS | FAN feature, provides notification to interested client | eONS | FAN feature, provides notification to interested client | SCAN Listener | Start & Monitor scan listener | Node Listener | Start & monitor the node listener (rdbms?) |
9. As you said Voting & OCR Disk resides in ASM Diskgroups, but as per startup sequence OCSSD starts first before than ASM, how is it possible?
How does OCSSD starts if voting disk & OCR resides in ASM Diskgroups?
You might wonder how CSSD, which is required to start the clustered ASM instance, can be started if voting disks are stored in ASM? This sounds like a chicken-and-egg problem: without access to the voting disks there is no CSS, hence the node cannot join the cluster. But without being part of the cluster, CSSD cannot start the ASM instance. To solve this problem the ASM disk headers have new metadata in 11.2: you can use kfed to read the header of an ASM disk containing a voting disk. The kfdhdb.vfstart and kfdhdb.vfend fields tell CSS where to find the voting file. This does not require the ASM instance to be up. Once the voting disks are located, CSS can access them and joins the cluster.
Source: Pro Oracle Database 11g RAC on Linux- Martin Bach … – Amazon.com
10. How does SCAN works?

1. Client Connected through SCAN name of the cluster (remember all three IP addresses round robin resolves to same Host name (SCAN Name), here in this case our scan name is cluster01-scan.cluster01.example.com 2. The request reaches to DNS server in your corp and then resolves to one of the node out of three. a. If GNS (Grid Naming service or domain is configured) that is a subdomain configured in the DNS entry for to resolve cluster address the request will be handover to GNS (gnsd) 3. Here in our case assume there is no GNS, now the with the help of SCAN listeners where end points are configured to database listener. 4. Database Listeners listen the request and then process further. 5. In case of node addition, Listener 4, client need not to know or need not change any thing from their tns entry (address of 4th node/instance) as they just using scan IP. 6. Same case even in the node deletion.
11. What is GNS?
Grid Naming service is alternative service to DNS , which will act as a sub domain in your DNS but managed by Oracle, with GNS the connection is routed to the cluster IP and manages internally.
12. What is GPNP?
Grid Plug and Play along with GNS provide dynamic
In previous releases, adding or removing servers in a cluster required extensive manual preparation.
In Oracle Database 11g Release 2, GPnP allows each node to perform the following tasks dynamically: * Negotiating appropriate network identities for itself * Acquiring additional information from a configuration profile * Configuring or reconfiguring itself using profile data, making host names and addresses resolvable on the network
For example a domain should contain * –Cluster name: cluster01 * –Network domain: example.com * –GPnP domain: cluster01.example.com
To add a node, simply connect the server to the cluster and allow the cluster to configure the node.
To make it happen, Oracle uses the profile located in $GI_HOME/gpnp/profiles/peer/profile.xml which contains the cluster resources, for example disk locations of ASM. etc.
So this profile will be read local or from the remote machine when plugged into cluster and dynamically added to cluster.
13. What are the file types that ASM support and keep in disk groups? Control files | Flashback logs | Data Pump dump sets | Data files | DB SPFILE | Data Guard configuration | Temporary data files | RMAN backup sets | Change tracking bitmaps | Online redo logs | RMAN data file copies | OCR files | Archive logs | Transport data files | ASM SPFILE |
14. List Key benefits of ASM? * Stripes files rather than logical volumes * Provides redundancy on a file basis * Enables online disk reconfiguration and dynamic rebalancing * Reduces the time significantly to resynchronize a transient failure by tracking changes while disk is offline * Provides adjustable rebalancing speed * Is cluster-aware * Supports reading from mirrored copy instead of primary copy for extended clusters * Is automatically installed as part of the Grid Infrastructure
15. List key benefits of Oracle Grid Infrastructure?
16. List some of the background process that used in ASM? Process | Description | RBAL | Opens all device files as part of discovery and coordinates the rebalance activity | ARBn | One or more slave processes that do the rebalance activity | GMON | Responsible for managing the disk-level activities such as drop or offline and advancing the ASM disk group compatibility | MARK | Marks ASM allocation units as stale when needed | Onnn | One or more ASM slave processes forming a pool of connections to the ASM instance for exchanging messages | PZ9n | One or more parallel slave processes used in fetching data on clustered ASM installation from GV$ views |
13. What is node listener?
In 11gr2 the listeners will run from Grid Infrastructure software home * The node listener is a process that helps establish network connections from ASM clients to the ASM instance. * Runs by default from the Grid $ORACLE_HOME/bin directory * Listens on port 1521 by default * Is the same as a database instance listener * Is capable of listening for all database instances on the same machine in addition to the ASM instance * Can run concurrently with separate database listeners or be replaced by a separate database listener * Is named tnslsnr on the Linux platform
15. What is SCAN listener?
A scan listener is something that additional to node listener which listens the incoming db connection requests from the client which got through the scan IP, it got end points configured to node listener where it routes the db connection requests to particular node listener.
16. What is the difference between CRSCTL and SRVCTL? crsctl manages clusterware-related operations: * Starting and stopping Oracle Clusterware * Enabling and disabling Oracle Clusterware daemons * Registering cluster resources srvctl manages Oracle resource–related operations: * Starting and stopping database instances and services * Also from 11gR2 manages the cluster resources like network,vip,disks etc
17. How to control Oracle Clusterware?
To start or stop Oracle Clusterware on a specific node:
# crsctl stop crs
# crsctl start crs
To enable or disable Oracle Clusterware on a specific node:
# crsctl enable crs
# crsctl disable crs
19. How to check the cluster (all nodes) status?
To check the viability of Cluster Synchronization Services (CSS) across nodes:
$ crsctl check cluster
CRS-4537: Cluster Ready Services is online
CRS-4529: Cluster Synchronization Services is online
CRS-4533: Event Manager is online
20. How to check the cluster (one node) status?
$ crsctl check crs
CRS-4638: Oracle High Availability Services is online
CRS-4537: Cluster Ready Services is online
CRS-4529: Cluster Synchronization Services is online
CRS-4533: Event Manager is online
21. How to find Voting Disk location?
•To determine the location of the voting disk:
# crsctl query css votedisk
## STATE File Universal Id File Name Disk group
– —– —————– ———- ———-
1. ONLINE 8c2e45d734c64f8abf9f136990f3daf8 (ASMDISK01) [DATA]
2. ONLINE 99bc153df3b84fb4bf071d916089fd4a (ASMDISK02) [DATA]
3. ONLINE 0b090b6b19154fc1bf5913bc70340921 (ASMDISK03) [DATA]
Located 3 voting disk(s).
22. How to find Location of OCR? * cat /etc/oracle/ocr.loc ocrconfig_loc=+DATA local_only=FALSE * #OCRCHECK (also about OCR integrity)
23. List some background process that used in ASM Instances? Process | Description | RBAL | Opens all device files as part of discovery and coordinates the rebalance activity | ARBn | One or more slave processes that do the rebalance activity | GMON | Responsible for managing the disk-level activities such as drop or offline and advancing the ASM disk group compatibility | MARK | Marks ASM allocation units as stale when needed | Onnn | One or more ASM slave processes forming a pool of connections to the ASM instance for exchanging messages | PZ9n | One or more parallel slave processes used in fetching data on clustered ASM installation from GV$ views |
24. What are types of ASM Mirroring? Disk Group Type | Supported Mirroring Levels | Default Mirroring Level | External redundancy | Unprotected (None) | Unprotected (None) | Normal redundancy | Two-wayThree-wayUnprotected (None) | Two-way | High redundancy | Three-way | Three-way |
25. What is ASM Striping?
ASM can use variable size data extents to support larger files, reduce memory requirements, and improve performance.
Each data extent resides on an individual disk.
Data extents consist of one or more allocation units.
The data extent size is: * Equal to AU for the first 20,000 extents (0–19999) * Equal to 4 × AU for the next 20,000 extents (20000–39999) * Equal to 16 × AU for extents above 40,000
ASM stripes files using extents with a coarse method for load balancing or a fine method to reduce latency. * Coarse-grained striping is always equal to the effective AU size. * Fine-grained striping is always equal to 128 KB.
26. How many ASM Diskgroups can be created under one ASM Instance?
ASM imposes the following limits: * 63 disk groups in a storage system * 10,000 ASM disks in a storage system * Two-terabyte maximum storage for each ASM disk (non-Exadata) * Four-petabyte maximum storage for each ASM disk (Exadata) * 40-exabyte maximum storage for each storage system * 1 million files for each disk group * ASM file size limits (database limit is 128 TB): 1. External redundancy maximum file size is 140 PB. 2. Normal redundancy maximum file size is 42 PB. 3. High redundancy maximum file size is 15 PB.
27. How to find the cluster network settings?
To determine the list of interfaces available to the cluster:
$ oifcfg iflist –p -n
To determine the public and private interfaces that have been configured:
$ oifcfg getif eth0 192.0.2.0 global public eth1 192.168.1.0 global cluster_interconnect
To determine the Virtual IP (VIP) host name, VIP address, VIP subnet mask, and VIP interface name:
$ srvctl config nodeapps -a
VIP exists.:host01
VIP exists.: /192.0.2.247/192.0.2.247/255.255.255.0/eth0
…
28. How to change Public or VIP Address in RAC Cluster?
Click here for details
29. How to change Cluster interconnect in RAC?
On a single node in the cluster, add the new global interface specification:
$ oifcfg setif -global eth2/192.0.2.0:cluster_interconnect
Verify the changes with oifcfg getif and then stop Clusterware on all nodes by running the following command as root on each node:
# oifcfg getif
# crsctl stop crs
Assign the network address to the new network adapters on all nodes using ifconfig:
#ifconfig eth2 192.0.2.15 netmask 255.255.255.0 broadcast 192.0.2.255
Remove the former adapter/subnet specification and restart Clusterware:
$ oifcfgdelif -global eth1/192.168.1.0
# crsctl start crs
30. Managing or Modifying SCAN in Oracle RAC?
To add a SCAN VIP resource:
$ srvctl add scan -n cluster01-scan
To remove Clusterware resources from SCAN VIPs:
$ srvctl remove scan [-f]
To add a SCAN listener resource:
$ srvctl add scan_listener
$ srvctl add scan_listener -p 1521
To remove Clusterware resources from all SCAN listeners:
$ srvctl remove scan_listener [-f]
31. How to check the node connectivity in Oracle Grid Infrastructure?
$ cluvfy comp nodecon -n all –verbose
32. Can I stop all nodes in one command? Meaning that stopping whole cluster ?
In 10g its not possible, where in 11g it is possible
[root@pic1]# crsctl start cluster -all
[root@pic2]# crsctl stop cluster –all
33. What is OLR? Which of the following statements regarding the Oracle Local Registry (OLR) is true?
1.Each cluster node has a local registry for node-specific resources.
2.The OLR should be manually created after installing Grid Infrastructure on each node in the cluster.
3.One of its functions is to facilitate Clusterware startup in situations where the ASM stores the OCR and voting disks.
4.You can check the status of the OLR using ocrcheck.
34. What is runfixup.sh script in Oracle Clusterware 11g release 2 installation
With Oracle Clusterware 11g release 2, Oracle Universal Installer (OUI) detects when the minimum requirements for an installation are not met, and creates shell scripts, called fixup scripts, to finish incomplete system configuration steps. If OUI detects an incomplete task, then it generates fixup scripts (runfixup.sh). You can run the fixup script after you click the Fix and Check Again Button.
The Fixup script does the following:
If necessary sets kernel parameters to values required for successful installation, including: * Shared memory parameters. * Open file descriptor and UDP send/receive parameters.
Sets permissions on the Oracle Inventory (central inventory) directory. Reconfigures primary and secondary group memberships for the installation owner, if necessary, for the Oracle Inventory directory and the operating system privileges groups. * Sets shell limits if necessary to required values.
35. How to stop whole cluster with single command crsctl stop cluster (possible only from 11gr2), please note crsctl commands becomes global now, if you do not specify node specifically the command executed globally for example crsctl stop crs (stops in all crs resource in all nodes) crsctl stop crs –n <ndeoname) (stops only in specified node)
36. CRS is not starting automatically after a node reboot, what you do to make it happen? crsctl enable crs (as root) to disable crsctl disable crs (as root)
37. What are server pools in 11gr2?
Read here -- http://oracle-info.com/dbahelper/
38. What is policy managed databases in RAC?
Read here
39. What is Load balancing & how does it work?
You must read here & here
40. Describe high level Steps to convert single instance to RAC?
Read here
41. What is the difference between TAF and FAN & FCF? at what conditions you use them?
1) TAF with tnsnames a feature of Oracle Net Services for OCI8 clients. TAF is transparent application failover which will move a session to a backup connection if the session fails. With Oracle 10g Release 2, you can define the TAF policy on the service using dbms_service package. It will only work with OCI clients. It will only move the session and if the parameter is set, it will failover the select statement. For insert, update or delete transactions, the application must be TAF aware and roll back the transaction. YES, you should enable FCF on your OCI client when you use TAF, it will make the failover faster.
Note: TAF will not work with JDBC thin.
2) FAN with tnsnames with aq notifications true
FAN is a feature of Oracle RAC which stands for Fast Application Notification. This allows the database to notify the client of any change (Node up/down, instance up/down, database up/down). For integrated clients, inflight transactions are interrupted and an error message is returned. Inactive connections are terminated.
FCF is the client feature for Oracle Clients that have integrated with FAN to provide fast failover for connections. Oracle JDBC Implicit Connection Cache, Oracle Data Provider for .NET (ODP.NET) and Oracle Call Interface are all integrated clients which provide the Fast Connection Failover feature.
3) FCF, along with FAN when using connection pools
FCF is a feature of Oracle clients that are integrated to receive FAN events and abort inflight transactions, clean up connections when a down event is received as well as create new connections when a up event is received. Tomcat or JBOSS can take advantage of FCF if the Oracle connection pool is used underneath. This can be either UCP (Universal Connection Pool for JAVA) or ICC (JDBC Implicit Connection Cache). UCP is recommended as ICC will be deprecated in a future release.
4) ONS, with clusterware either FAN/FCF
ONS is part of the clusterware and is used to propagate messages both between nodes and to application-tiers
ONS is the foundation for FAN upon which is built FCF.
RAC uses FAN to publish configuration changes and LBA events. Applications can react as those published events in two way :
– by using ONS api (you need to program it)
– by using FCF (automatic by using JDBC implicit connection cache on the application server) you can also respond to FAN event by using server-side callout but this on the server side (as their name suggests it)
Relationship between FAN/FCF/ONS
ONS –> FAN –> FCF
ONS -> send/receive messages on local and remote nodes.
FAN -> uses ONS to notify other processes about changes in configuration of service level
FCF -> uses FAN information working with conection pools JAVA and others.
42. Can you add voting disk online? Do you need voting disk backup?
Yes, as per documentation, if you have multiple voting disk you can add online, but if you have only one voting disk , by that cluster will be down as its lost you just need to start crs in exclusive mode and add the votedisk using crsctl add votedisk <path>
43. You have lost OCR disk, what is your next step?
The cluster stack will be down due to the fact that cssd is unable to maintain the integrity, this is true in 10g, From 11gR2 onwards, the crsd stack will be down, the hasd still up and running. You can add the ocr back by restoring the automatic backup or import the manual backup,
Read complete steps here
44. What happens when ocssd fails, what is node eviction? how does node eviction happens? For all answer will be same.
Cluster integrity and cluster membership will be governed by occsd (oracle cluster synchronization daemon) monitors the nodes using 2 communication channels:
- Private Interconnect aka Network Heartbeat
- Voting Disk based communication aka Disk Heartbeat
Network heartbeat:-
Each node in the cluster is “pinged” every second * Nodes must respond in css_misscount time (defaults to 30 secs.) – Reducing the css_misscount time is generally not supported * Network heartbeat failures will lead to node evictions * CSSD-log: [date / time] [CSSD][1111902528] clssnmPollingThread: node mynodename (5) at 75% heartbeat fatal, removal in 6.7 sec
Disk Heartbeat:-
Each node in the cluster “pings” (r/w) the Voting Disk(s) every second * Nodes must receive a response in (long / short) diskTimeout time – IF I/O errors indicate clear accessibility problems timeout is irrelevant * Disk heartbeat failures will lead to node evictions * CSSD-log: … [CSSD] [1115699552] >TRACE: clssnmReadDskHeartbeat:node(2) is down. rcfg(1) wrtcnt(1) LATS(63436584) Disk lastSeqNo(1)
Now, we know with above possibilities (network, disk heartbeat failures can lead to node eviction, but sometime when the server/occsd/resource request also makes the node get evicted which are extreme cases)
Why nodes should be evicted?
Evicting (fencing) nodes is a preventive measure (it’s a good thing)! * Nodes are evicted to prevent consequences of a split brain: – Shared data must not be written by independently operating nodes – The easiest way to prevent this is to forcibly remove a node from the cluster
How are nodes evicted? – STONITH
Once it is determined that a node needs to be evicted, * A “kill request” is sent to the respective node(s) – Using all (remaining) communication channels * A node (CSSD) is requested to “kill itself” – “STONITH like” – “STONITH” foresees that a remote node kills the node to be evicted
EXAMPLE: Voting Disk Failure
Voting Disks and heartbeat communication is used to determine the node * In a 2 node cluster, the node with the lowest node number should survive * In a n-node cluster, the biggest sub-cluster should survive (votes based)
EXAMPLE: Network heartbeat failure * The network heartbeat between nodes has failed – It is determined which nodes can still talk to each other – A “kill request” is sent to the node(s) to be evicted * Using all (remaining) communication channels Voting Disk(s) * A node is requested to “kill itself”; executer: typically CSSD
EXAMPLE: What if CSSD is stuck or server itself is not responding?
A node is requested to “kill itself” * BUT CSSD is “stuck” or “sick” (does not execute) – e.g.: – CSSD failed for some reason – CSSD is not scheduled within a certain margin
OCSSDMONITOR (was: oprocd) will take over and execute
EXAMPLE: Cluster member (rac instance) can request a to kill another member (RAC Instance)
A cluster member (rac instance ) can request a kill another member in order to protect the data integrity, in such cases like control file progress record not written proper by the failure instance(read here) , then occsd tries to kill that member, if not possible its tries to evict the node. 11gR2 Changes –> Important, in 11GR2, the fencing (eviction) does not to reboot. * Until Oracle Clusterware 11.2.0.2, fencing (eviction) meant “re-boot” * With Oracle Clusterware 11.2.0.2, re-boots will be seen less, because: – Re-boots affect applications that might run an a node, but are not protected – Customer requirement: prevent a reboot, just stop the cluster – implemented…
How does this works?
With Oracle Clusterware 11.2.0.2, re-boots will be seen less: Instead of fast re-booting the node, a graceful shutdown of the cluster stack is attempted * It starts with a failure – e.g. network heartbeat or interconnect failure * Then IO issuing processes are killed; it is made sure that no IO process remains – For a RAC DB mainly the log writer and the database writer are of concern * Once all IO issuing processes are killed, remaining processes are stopped – IF the check for a successful kill of the IO processes, fails → reboot * Once all remaining processes are stopped, the stack stops itself with a “restart flag” * OHASD will finally attempt to restart the stack after the graceful shutdown Exception to above:- * IF the check for a successful kill of the IO processes fails → reboot * IF CSSD gets killed during the operation → reboot * IF cssdmonitor (oprocd replacement) is not scheduled → reboot * IF the stack cannot be shutdown in “short_disk_timeout”-seconds → reboot
45. What is virtual IP and how does it works?
The goal is application availability with the shortest disruption time possible.
When a node fails, the VIP associated with it is automatically failed over to some other node. When this occurs, the following things happen. Vip resources in CRS (ora.node.vip)
(1) VIP detects public network failure which generates a FAN event. ( A FAN event is an fast application notification event and ONS captures and publishes to the subscriber in RAC the subscriber can be listener)
(2) the new node re-arps (see arpa) the world indicating a new MAC address for the IP.
(3) connected clients subscribing to FAN immediately receive ORA-3113 error or equivalent. Those not subscribing to FAN will eventually time out.
(4) New connection requests rapidly traverse the tnsnames.ora address list skipping over the dead nodes, instead of having to wait on TCP-IP timeouts (default 10 mins)
Without using VIPs or FAN, clients connected to a node that died will often wait for a TCP timeout period (which can be up to 10 min) before getting an error. As a result, you don’t really have a good HA solution without using VIPs and FAN. The easiest way to use FAN is to use an integrated client with Fast Connection Failover (FCF) such as JDBC, OCI, or ODP.NET.
46. Describe some rac wait events you experienced?
Oracle RAC Wait events and this table,

47. Can you modify VIP address after your cluster installation?
Yes, read here
48. How do you interpret AWR report in RAC instances, what sections in awr report for rac instances are most important?

Update 12-May-2013, Some practical questions added here
1. Viewing Contents in OCR/Voting disks There are three possible ways to view the OCR contents. a. OCRDUMP (or) b. crs_stat -p (or) c. By using strings. Voting disk contents are not persistent and are not required to view the contents, because the voting disk contents will be overwritten. if still need to view, strings are used.
2. Server pools – Read in my blog
3. Verifying Cluster Interconnect Cluster interconnects can be verified by: i. oifcfg getif ii. From AWR Report. iii. show parameter cluster_interconnect iv. srvctl config network
4. Does scan IP required or we can disable it SCAN IP can be disabled if not required. However SCAN IP is mandatory during the RAC installation. Enabling/disabling SCAN IP is mostly used in oracle apps environment by the concurrent manager (kind of job scheduler in oracle apps). To disable the SCAN IP, i. Do not use SCAN IP at the client end. ii. Stop scan listener srvctl stop scan_listener iii. Stop scan srvctl stop scan (this will stop the scan vip's) iv. Disable scan and disable scan listener srvctl disable scan
5. Migrating to new Diskgroup scenarious
a. Case 1: Migrating disk group from one storage to other with same name 1. Consider the disk group is DATA, 2. Create new disks in DATA pointing towards the new storage (EMC), a) Partioning provisioning done by storage and they give you the device name or mapper like /dev/mapper/asakljdlas 3. Add the new disk to diskgroup DATA a) Alter diskgroup data add disk '/dev/mapper/asakljdlas' 3. drop the old disks from DATA with which rebalancing is done automatically. If you want you can the rebalance by alter system set asm_power_limit =12 for full throttle. alter diskgroup data drop disk 'path to hitachi storage' Note: you can get the device name in v$asm_disk in path column. 4. Request SAN team to detach the old Storage (HITACHI).

b. Case 2: Migrating disk group from one to another with different diskgroup name. 1) Create the Disk group with new name in the new storage. 2) Create the spfile in new diskgroup and change the parameter scope = spfile for control files etc. 3) Take a control file backup in format +newdiskgroup 4) Shutdown the db, startup nomount the database 5) restore the control file from backup (now the control will restore to new diskgroup) 6) Take the RMAN backup as copy of all the databases with new format. RMAN&gt; backup database as copy format '+newdiskgroup name' ; 3) RMAN&gt; Switch database to copy. 4) Verify dba_data_files,dba_temp_files, v$log that all files are pointing to new diskgroup name.

c. Case 3: Migrating disk group to new storage but no additional diskgroup given 1) Take the RMAN backup as copy of all the databases with new format and place it in the disk. 2) Prepare rename commands from v$log ,v$datafile etc (dynamic queries) 3) Take a backup of pfile and modify the following referring to new diskgroup name .control_files .db_create_file_dest .db_create_online_log_dest_1 .db_create_online_log_dest_2 .db_recovery_file_des 4) stop the database 5) Unmount the diskgroup asmcmd umount ORA_DATA 6) use asmcmd renamedg (11gr2 only) command to rename to new diskgroup renamedg phase=both dgname=ORA_DATA newdgname=NEW_DATA verbose=true 7) mount the diskgroup asmcmd mount NEW_DATA 8) start the database in mount with new pfile taken backup in step 3 9) Run the rename file scripts generated at step2 9) Add the diskgroup to cluster the cluster (if using rac) srvctl modify database -d orcl -p +NEW_FRA/orcl/spfileorcl.ora srvctl modify database -d orcl -a "NEW_DATA" srvctl config database -d orcl srvctl start database -d orcl 10) Delete the old diskgroup from cluster crsctl delete resource ora.ORA_DATA.dg 11) Open the database.
7. Database rename in RAC, what could be the checklist for you? a. Take the outputs of all the services that are running on the databases. b. set cluster_database=FALSE c. Drop all the services associated with the database. d. Stop the database e. Startup mount f. Use nid to change the DB Name. Generic question, If using ASM the usual location for the datafile would be +DATA/datafile/OLDDBNAME/system01.dbf' Does NID changes this path too? to reflect the new db name? Yes it will, by using proper directory structure it will create a links to original directory structure. +DATA/datafile/NEWDBNAME/system01.dbf' this has to be tested, We dont have test bed, but thanks to Anji who confirmed it will

g. Change the parameters according to the new database name h. Change the password file. i. Stop the database. j. Mount the database k. Open database with Reset logs l. Create spfile from pfile. m. Add database to the cluster. n. Create the services that are dropped in prior to rename. o. Bounce the database.
8.How to find the database in which particular service is attached to when you have a large number of databases running in the server, you cannot check one by one manually
Write a shell script to read the database name from oratab and iterate the loop taking inpt as DB name in srvctl to get the result.
#!/bin/ksh
ORACLE_HOME=<crs_home>
PATH=$ORACLE_HOME/bin:$PATH
LD_LIBRARY_PATH=${SAVE_LLP}:${ORACLE_HOME}/lib export TNS_ADMIN ORACLE_HOME PATH LD_LIBRARY_PATH for INSTANCE in `cat /etc/oratab|grep -v “^#”|cut -f1 -d: -s` do export ORACLE_SID=$INSTANCE echo `srvctl status service -d $INSTANCE -s $1| grep -i “is running”` done -------------------------------------------------
9. Difference between OHAS and CRS
OHAS is complete cluster stack which includes some kernel level tasks like managing network,time synchronization, disks etc, where the CRS has the ability to manage the resources like database,listeners,applications, etc With both of this Oracle provides the high availability clustering services rather only affinity to databases.
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What is RAC? What is the benefit of RAC over single instance database?
In Real Application Clusters environments, all nodes concurrently execute transactions against the same database. Real Application Clusters coordinates each node’s access to the shared data to provide consistency and integrity.
Benefits:
Improve response time
Improve throughput
High availability
Transparency
What is Oracle RAC One Node?
Oracle RAC one Node is a single instance running on one node of the cluster while the 2nd node is in cold standby mode. If the instance fails for some reason then RAC one node detect it and restart the instance on the same node or the instance is relocate to the 2nd node incase there is failure or fault in 1st node. The benefit of this feature is that it provides a cold failover solution and it automates the instance relocation without any downtime and does not need a manual intervention. Oracle introduced this feature with the release of 11gR2 (available with Enterprise Edition).
Real Application Clusters
Oracle RAC is a cluster database with a shared cache architecture that overcomes the limitations of traditional shared-nothing and shared-disk approaches to provide a highly scalable and available database solution for all your business applications. Oracle RAC provides the foundation for enterprise grid computing.
Oracle’s Real Application Clusters (RAC) option supports the transparent deployment of a single database across a cluster of servers, providing fault tolerance from hardware failures or planned outages. Oracle RAC running on clusters provides Oracle’s highest level of capability in terms of availability, scalability, and low-cost computing.
One DB opened by multipe instances so the the db ll be Highly Available if an instance crashes.
Cluster Software. Oracles Clusterware or products like Veritas Volume Manager are required to provide the cluster support and allow each node to know which nodes belong to the cluster and are available and with Oracle Cluterware to know which nodes have failed and to eject then from the cluster, so that errors on that node can be cleared.
Oracle Clusterware has two key components Cluster Registry OCR and Voting Disk.
The cluster registry holds all information about nodes, instances, services and ASM storage if used, it also contains state information ie they are available and up or similar.
The voting disk is used to determine if a node has failed, i.e. become separated from the majority. If a node is deemed to no longer belong to the majority then it is forcibly rebooted and will after the reboot add itself again the the surviving cluster nodes.
Advantages of RAC (Real Application Clusters)
Reliability – if one node fails, the database won’t fail
Availability – nodes can be added or replaced without having to shutdown the database
Scalability – more nodes can be added to the cluster as the workload increases
What is a virtual IP address or VIP?
A virtual IP address or VIP is an alternate IP address that the client connections use instead of the standard public IP address. To configure VIP address, we need to reserve a spare IP address for each node, and the IP addresses must use the same subnet as the public network.
What is the use of VIP?
If a node fails, then the node’s VIP address fails over to another node on which the VIP address can accept TCP connections but it cannot accept Oracle connections.
Give situations under which VIP address failover happens:-
VIP addresses failover happens when the node on which the VIP address runs fails, all interfaces for the VIP address fails, all interfaces for the VIP address are disconnected from the network.
Using virtual IP we can save our TCP/IP timeout problem because Oracle notification service maintains communication between each nodes and listeners.
What is the significance of VIP address failover?
When a VIP address failover happens, Clients that attempt to connect to the VIP address receive a rapid connection refused error .They don’t have to wait for TCP connection timeout messages.
What is voting disk?
Voting Disk is a file that sits in the shared storage area and must be accessible by all nodes in the cluster. All nodes in the cluster registers their heart-beat information in the voting disk, so as to confirm that they are all operational. If heart-beat information of any node in the voting disk is not available that node will be evicted from the cluster. The CSS (Cluster Synchronization Service) daemon in the clusterware maintains the heart beat of all nodes to the voting disk. When any node is not able to send heartbeat to voting disk, then it will reboot itself, thus help avoiding the split-brain syndrome.
For high availability, Oracle recommends that you have a minimum of three or odd number (3 or greater) of votingdisks.
Voting Disk – is file that resides on shared storage and Manages cluster members. Voting disk reassigns cluster ownership between the nodes in case of failure.
The Voting Disk Files are used by Oracle Clusterware to determine which nodes are currently members of the cluster. The voting disk files are also used in concert with other Cluster components such as CRS to maintain the clusters integrity.
Oracle Database 11g Release 2 provides the ability to store the voting disks in ASM along with the OCR. Oracle Clusterware can access the OCR and the voting disks present in ASM even if the ASM instance is down. As a result CSS can continue to maintain the Oracle cluster even if the ASM instance has failed.
How many voting disks are you maintaining ? http://www.toadworld.com/KNOWLEDGE/KnowledgeXpertforOracle/tabid/648/TopicID/RACR2ARC6/Default.aspx By default Oracle will create 3 voting disk files in ASM.
Oracle expects that you will configure at least 3 voting disks for redundancy purposes. You should always configure an odd number of voting disks >= 3. This is because loss of more than half your voting disks will cause the entire cluster to fail.
You should plan on allocating 280MB for each voting disk file. For example, if you are using ASM and external redundancy then you will need to allocate 280MB of disk for the voting disk. If you are using ASM and normal redundancy you will need 560MB.
Why we need to keep odd number of voting disks ?
Oracle expects that you will configure at least 3 voting disks for redundancy purposes. You should always configure an odd number of voting disks >= 3. This is because loss of more than half your voting disks will cause the entire cluster to fail.
What are Oracle RAC software components?
Oracle RAC is composed of two or more database instances. They are composed of Memory structures and background processes same as the single instance database.Oracle RAC instances use two processes GES(Global Enqueue Service), GCS(Global Cache Service) that enable cache fusion.Oracle RAC instances are composed of following background processes:
ACMS—Atomic Controlfile to Memory Service (ACMS)
GTX0-j—Global Transaction Process
LMON—Global Enqueue Service Monitor
LMD—Global Enqueue Service Daemon
LMS—Global Cache Service Process
LCK0—Instance Enqueue Process
RMSn—Oracle RAC Management Processes (RMSn)
RSMN—Remote Slave Monitor
What are Oracle Clusterware processes for 10g ?
Cluster Synchronization Services (ocssd) — Manages cluster node membership and runs as the oracle user; failure of this process results in cluster restart.
Cluster Ready Services (crsd) — The crs process manages cluster resources (which could be a database, an instance, a service, a Listener, a virtual IP (VIP) address, an application process, and so on) based on the resource’s configuration information that is stored in the OCR. This includes start, stop, monitor and failover operations. This process runs as the root user
Event manager daemon (evmd) —A background process that publishes events that crs creates.
Process Monitor Daemon (OPROCD) —This process monitor the cluster and provide I/O fencing. OPROCD performs its check, stops running, and if the wake up is beyond the expected time, then OPROCD resets the processor and reboots the node. An OPROCD failure results in Oracle Clusterware restarting the node. OPROCD uses the hangcheck timer on Linux platforms.
RACG (racgmain, racgimon) —Extends clusterware to support Oracle-specific requirements and complex resources. Runs server callout scripts when FAN events occur.
What are Oracle database background processes specific to RAC?
LMS—Global Cache Service Process
LMD—Global Enqueue Service Daemon
LMON—Global Enqueue Service Monitor
LCK0—Instance Enqueue Process
Oracle RAC instances use two processes, the Global Cache Service (GCS) and the Global Enqueue Service (GES). The GCS and GES maintain records of the statuses of each data file and each cached block using a Global Resource Directory (GRD). The GRD contents are distributed across all of the active instances.
What is Cache Fusion?
Transfor of data across instances through private interconnect is called cachefusion.Oracle RAC is composed of two or more instances. When a block of data is read from datafile by an instance within the cluster and another instance is in need of the same block,it is easy to get the block image from the insatnce which has the block in its SGA rather than reading from the disk. To enable inter instance communication Oracle RAC makes use of interconnects. The Global Enqueue Service(GES) monitors and Instance enqueue process manages the cahce fusion
What is SCAN? (11gR2 feature)
Single Client Access Name (SCAN) is s a new Oracle Real Application Clusters (RAC) 11g Release 2 feature that provides a single name for clients to access an Oracle Database running in a cluster. The benefit is clients using SCAN do not need to change if you add or remove nodes in the cluster.
SCAN provides a single domain name via (DNS), allowing and-users to address a RAC cluster as-if it were a single IP address. SCAN works by replacing a hostname or IP list with virtual IP addresses (VIP).
Single client access name (SCAN) is meant to facilitate single name for all Oracle clients to connect to the cluster database, irrespective of number of nodes and node location. Until now, we have to keep adding multiple address records in all clients tnsnames.ora, when a new node gets added to or deleted from the cluster.
Single Client Access Name (SCAN) eliminates the need to change TNSNAMES entry when nodes are added to or removed from the Cluster. RAC instances register to SCAN listeners as remote listeners. Oracle recommends assigning 3 addresses to SCAN, which will create 3 SCAN listeners, though the cluster has got dozens of nodes.. SCAN is a domain name registered to at least one and up to three IP addresses, either in DNS (Domain Name Service) or GNS (Grid Naming Service). The SCAN must resolve to at least one address on the public network. For high availability and scalability, Oracle recommends configuring the SCAN to resolve to three addresses. http://www.freeoraclehelp.com/2011/12/scan-setup-for-oracle-11g-release211gr2.html What are SCAN components in a cluster?
1.SCAN Name
2.SCAN IPs (3)
3.SCAN Listeners (3)
What is FAN?
Fast application Notification as it abbreviates to FAN relates to the events related to instances,services and nodes.This is a notification mechanism that Oracle RAc uses to notify other processes about the configuration and service level information that includes service status changes such as,UP or DOWN events.Applications can respond to FAN events and take immediate action.
What is TAF?
TAF (Transparent Application Failover) is a configuration that allows session fail-over between different nodes of a RAC database cluster.
Transparent Application Failover (TAF). If a communication link failure occurs after a connection is established, the connection fails over to another active node. Any disrupted transactions are rolled back, and session properties and server-side program variables are lost. In some cases, if the statement executing at the time of the failover is a Select statement, that statement may be automatically re-executed on the new connection with the cursor positioned on the row on which it was positioned prior to the failover.
After an Oracle RAC node crashes—usually from a hardware failure—all new application transactions are automatically rerouted to a specified backup node. The challenge in rerouting is to not lose transactions that were “in flight” at the exact moment of the crash. One of the requirements of continuous availability is the ability to restart in-flight application transactions, allowing a failed node to resume processing on another server without interruption. Oracle’s answer to application failover is a new Oracle Net mechanism dubbed Transparent Application Failover. TAF allows the DBA to configure the type and method of failover for each Oracle Net client.
TAF architecture offers the ability to restart transactions at either the transaction (SELECT) or session level.
What are the requirements for Oracle Clusterware?
1. External Shared Disk to store Oracle Cluster ware file (Voting Disk and Oracle Cluster Registry – OCR)
2. Two netwrok cards on each cluster ware node (and three set of IP address) -
Network Card 1 (with IP address set 1) for public network
Network Card 2 (with IP address set 2) for private network (for inter node communication between rac nodes used by clusterware and rac database)
IP address set 3 for Virtual IP (VIP) (used as Virtual IP address for client connection and for connection failover)
3. Storage Option for OCR and Voting Disk – RAW, OCFS2 (Oracle Cluster File System), NFS, …..
Which enable the load balancing of applications in RAC?
Oracle Net Services enable the load balancing of application connections across all of the instances in an Oracle RAC database.
How to find location of OCR file when CRS is down?
If you need to find the location of OCR (Oracle Cluster Registry) but your CRS is down.
When the CRS is down:
Look into “ocr.loc” file, location of this file changes depending on the OS:
On Linux: /etc/oracle/ocr.loc
On Solaris: /var/opt/oracle/ocr.loc
When CRS is UP:
Set ASM environment or CRS environment then run the below command: ocrcheck In 2 node RAC, how many NIC’s are r using ?
2 network cards on each clusterware node
Network Card 1 (with IP address set 1) for public network
Network Card 2 (with IP address set 2) for private network (for inter node communication between rac nodes used by clusterware and rac database)
In 2 node RAC, how many IP’s are r using ?
6 – 3 set of IP address
## eth1-Public: 2
## eth0-Private: 2
## VIP: 2
How to find IP’s information in RAC ?
Edit the /etc/hosts file as shown below:
# Do not remove the following line, or various programs
# that requires network functionality will fail.
127.0.0.1 localhost.localdomain localhost
## Public Node names
192.168.10.11 node1-pub.hingu.net node1-pub
192.168.10.22 node2-pub.hingu.net node2-pub
## Private Network (Interconnect)
192.168.0.11 node1-prv node1-prv
192.168.0.22 node2-prv node2-prv
## Private Network (Network Area storage)
192.168.1.11 node1-nas node1-nas
192.168.1.22 node2-nas node2-nas
192.168.1.33 nas-server nas-server
## Virtual IPs
192.168.10.111 node1-vip.hingu.net node1-vip
192.168.10.222 node2-vip.hingu.net node2-vip
What is difference between RAC ip addresses ?
Public IP adress is the normal IP address typically used by DBA and SA to manage storage, system and database. Public IP addresses are reserved for the Internet.
Private IP address is used only for internal clustering processing (Cache Fusion) (aka as interconnect). Private IP addresses are reserved for private networks.
VIP is used by database applications to enable fail over when one cluster node fails. The purpose for having VIP is so client connection can be failover to surviving nodes in case there is failure
Can application developer access the private ip ?
No. private IP address is used only for internal clustering processing (Cache Fusion) (aka as interconnect)
Oracle RAC Interview Questions (10g) Questions and Answers

What are Oracle Clusterware processes for 10g on Unix and Linux
Cluster Synchronization Services (ocssd) — Manages cluster node membership and runs as the oracle user; failure of this process results in cluster restart.
Cluster Ready Services (crsd) — The crs process manages cluster resources (which could be a database, an instance, a service, a Listener, a virtual IP (VIP) address, an application process, and so on) based on the resource’s configuration information that is stored in the OCR. This includes start, stop, monitor and failover operations. This process runs as the root user
Event manager daemon (evmd) —A background process that publishes events that crs creates.
Process Monitor Daemon (OPROCD) —This process monitor the cluster and provide I/O fencing. OPROCD performs its check, stops running, and if the wake up is beyond the expected time, then OPROCD resets the processor and reboots the node. An OPROCD failure results in Oracle Clusterware restarting the node. OPROCD uses the hangcheck timer on Linux platforms.
RACG (racgmain, racgimon) —Extends clusterware to support Oracle-specific requirements and complex resources. Runs server callout scripts when FAN events occur.
What are Oracle database background processes specific to RAC
•LMS—Global Cache Service Process
•LMD—Global Enqueue Service Daemon
•LMON—Global Enqueue Service Monitor
•LCK0—Instance Enqueue Process
To ensure that each Oracle RAC database instance obtains the block that it needs to satisfy a query or transaction, Oracle RAC instances use two processes, the Global Cache Service (GCS) and the Global Enqueue Service (GES). The GCS and GES maintain records of the statuses of each data file and each cached block using a Global Resource Directory (GRD). The GRD contents are distributed across all of the active instances.
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What are Oracle Clusterware Components
Voting Disk —
• Oracle RAC uses the voting disk to manage cluster membership by way of a health check and arbitrates cluster ownership among the instances in case of network failures. The voting disk must reside on shared disk.
• Central reference of all nodes and keeps the heart beat information between nodes in terms of votes
Oracle Cluster Registry (OCR) — Maintains cluster configuration information as well as configuration information about any cluster database within the cluster. The OCR must reside on shared disk that is accessible by all of the nodes in your cluster
Oracle Cluster Interconnect — In other words also called as private interconnect, with high speed gigabit channel or infiniband. which ishigh speed , low latency network connection attached to private switches rather the public interfaces. This will be used by cluster to provide node membership and also inter cluster communication (aka global cache services , transfer of blocks from one node to another)
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How do you backup the OCR
There is an automatic backup mechanism for OCR. The default location is:
$ORA_CRS_HOMEcdata”clustername”
To display Backups:
#ocrconfig -showbackup
To restore a backup:
#ocrconfig –restore
With Oracle RAC 10g Release 2 or later, you can also use the export command:
#ocrconfig -export -s online, and use -import option to restore the contents back.

With Oracle RAC 11g Release 1, you can do a manaual backup of the OCR with the command:
# ocrconfig –manualbackup

How do you backup voting disk & do you need to take a backup of voting Disk.
#dd if=voting_disk_name of=backup_file_name
Voting disk backup is not required since this is non-persistent data and just records about the node (cluster membership) availability, when you start the cluster it is empty.
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How do I identify the voting disk location
#crsctl query css votedisk
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How do I identify the OCR file location check /var/opt/oracle/ocr.loc or /etc/ocr.loc (depends upon platform) or #ocrcheck
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How to identify which version of Clusterware is running & active.
#crsctl query –activeversion
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Is ssh required for normal Oracle RAC operation?
“ssh” are not required for normal Oracle RAC operation. However “ssh” should be enabled for Oracle RAC and patchset installation.
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What is the purpose of Private Interconnect?
Clusterware uses the private interconnect for cluster synchronization (network heartbeat) and daemon communication between the the clustered nodes. This communication is based on the TCP protocol.
RAC uses the interconnect for cache fusion (UDP) and inter-process communication (TCP). Cache Fusion is the remote memory mapping of Oracle buffers, shared between the caches of participating nodes in the cluster.
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Why do we have a Virtual IP (VIP) in Oracle RAC?
Without using VIPs or FAN, clients connected to a node that died will often wait for a TCP timeout period (which can be up to 10 min) before getting an error. As a result, you don’t really have a good HA solution without using VIPs.
When a node fails, the VIP associated with it is automatically failed over to some other node and new node re-arps the world indicating a new MAC address for the IP. Subsequent packets sent to the VIP go to the new node, which will send error RST packets back to the clients. This results in the clients getting errors immediately.
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What do you do if you see GC CR BLOCK LOST in top 5 Timed Events in AWR Report?
This is most likely due to a fault in interconnect network.
Check netstat -s if you see “fragments dropped” or “packet reassemblies failed” , Work with your system administrator find the fault with network.
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How many nodes are supported in a RAC Database?
10g Release 2, support 100 nodes in a cluster using Oracle Clusterware, and 100 instances in a RAC database.
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How to debug srvctl?
Set the environmental variable SRVM_TRACE to true.. And start the instance with srvctl. Now you will get detailed error stack.
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what is the purpose of the ONS daemon?
The Oracle Notification Service (ONS) daemon is an daemon started by the CRS clusterware as part of the nodeapps. There is one ons daemon started per clustered node.
The Oracle Notification Service daemon receive a subset of published clusterware events via the local evmd and racgimon clusterware daemons and forward those events to application subscribers and to the local listeners.
This in order to facilitate:
a. the FAN or Fast Application Notification feature or allowing applications to respond to database state changes.
b. the 10gR2 Load Balancing Advisory, the feature that permit load balancing accross different rac nodes dependent of the load on the different nodes. The rdbms MMON is creating an advisory for distribution of work every 30seconds and forward it via racgimon and ONS to listeners and applications.
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what is the ora.rac1.GSD in crs_stat?
It is called Global Service Daemon, which is there for backward compatibility, in other words in Oracle 9i, the RAC is running with Veritas cluster and the GSD will be synchronizing the instance details to Cluster. You can add the 9i instances to Oracle 10g or 11g RAC Clusters
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What is GRD?
Global Resource directory , a common memory structures across SGA’s, in other words this is the combination of GCS/GES memory structures (infact synchronizing all the times through cluster interconnect messages). All the resources in the cluster group form a central repository called GRD. which is integrated and distributed across the nodes memory structures. Each instance masters some of the resources (buffer) based on their weightage and accessibility) and together all formed called GRD. Basically a combination of GES and GCS.
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What is Dynamic Remastering?
Every instance (node) owns the block (buffers) called master node for that blocks when accessed first time. If the other node requires the same, it has to send a request to the owning node to get the blocks (CR/CUR modes). If the requests are more than 50 in an hour the mastership will be transferred to the other node.
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What is Node Mastering?
The node which starts first in the cluster acts a master node, If this crashes the other nodes who detects first will be the master node for that cluster.
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What is cache fusion, Which background process manages it?
Other words called as Global cache services, Cache fusion is to manage the buffers with in local or the global and transfers from instance to another , basically LMS process take cares of the transfers, upon receive the message (BST/AST) it manages the lock escalation and descalation with help of Global Enqueue services (LMD/LMON/LCK )processes, process the buffer and made a copy (if required) and then transfer that buffer to requested instance via cluster interconnect.
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What is cache coherency which background process manages it?
Cache coherency means that the contents of the caches in different nodes are in well defined state with respect to each other, is a technique of keeping multiple copies of buffers consistent between different Oracle instances. LMS process manages this in terms of local/global lock levels or with Message queues (AST/BST)
How does instance recovery works in RAC databases?

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Can you change Private interconnect IP address or Ethernet interface after cluster installation?
Yes, we can, before to that we should stop the clusterware and use oifcfg tool to delete the old and set the new interfaces, for ex:
#oifcfg –getif
#oifcfg –delif
#oifcfg –setif
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Can you change the Virutal IP after you install clusterware installation?
Yes, its possible, but you have to run vipca or using srvctl, please see here for complete steps
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What is the Load Balancing Advisory?
To assist in the balancing of application workload across designated resources, Oracle Database 10g Release 2 provides the Load Balancing Advisory. This Advisory monitors the current workload activity across the cluster and for each instance where a service is active; it provides a percentage value of how much of the total workload should be sent to this instance as well as service quality flag.
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What is hangcheck timer used for ?
The hangcheck timer checks regularly the health of the system. If the system hangs or stop the node will be restarted automatically.
There are 2 key parameters for this module:
-> hangcheck-tick: this parameter defines the period of time between checks of system health. The default value is 60 seconds; Oracle recommends setting it to 30seconds.
-> hangcheck-margin: this defines the maximum hang delay that should be tolerated before hangcheck-timer resets the RAC node.
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Is the hangcheck timer still needed with Oracle RAC 10g?
Yes

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What files can I put on Linux OCFS2?
For optimal performance, you should only put the following files on Linux OCFS2:
- Datafiles
- Control Files
- Redo Logs
- Archive Logs
- Shared Configuration File (OCR)
- Voting File
- SPFILE
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What are various cluster file systems
OCFS2, Veritas Cluster Filesystems, NFS, ASM, etc.
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Does ASM cannot be used as Cluster filesystem.
Well yes, ASM is storage management provides storage mirroring,striping along with cluster filesystem capabilities, it also acts as volume manager eliminating the need of disk cache I/O layer from OS.
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Can I change the name of my cluster after I have created it when I am using Oracle Clusterware?
No, you must properly uninstall Oracle Clusterware and then re-install.
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What command would you use to check the availability of the RAC system? crs_stat -t -v (-t -v are optional)
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Can you have many database versions in the same RAC?
Yes, but Clusterware version must be greater than the greater database version.
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How do I identify the OCR file location check /var/opt/oracle/ocr.loc or /etc/ocr.loc ( depends upon platform) or #ocrcheck
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How do I identify the voting disk location
#crsctl query css votedisk
– this works only when the clusterware is up in 10g, where in CRS start up is not required

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What is TAF? How does it works.
Transparent application failover is the mechansim to provide high availability of the database services to the connections happens via TNS along with RAC specific scripts called racgmon etc.
For this we o Configure TNS entry for that service in both nodes o Update the remote listener parameter with the service name o Add service name to high availability stack i.e to CRS using srvctl srvctl add service –d dbname –servicename –p <preferrednode> -r<availablenode>
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What is FAN? How does it works
Fast application notification is different from the TAF, which commonly used to trap the failures of the services using ONS (oracle notification services) for example JDBC connection does not failover on TAF events, where ONS can be used here.

What are RAC based services? What are difference between normal database service and RAC services?
•Is a means of grouping sessions that are doing the same kind of work
•Provides single-system image instead of multiple instances image
•Is a part of the regular administration tasks that provide dynamic service-to-instance allocation
•Is the base for high availability of connections
•Provides a new performance-tuning dimension
•Normal services not maintained in data dictionaries where the Rac services maintained in data dictionary.
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What happens if one of the node is not able to access the voting disk?
The master node OCSSD in the instance verifies the votes in the voting disk periodically and ensure quorum is matched, if quorum is not matched then it posts the failure nodes OCSSD to evict the cluster.
Or Node OCSSD recognises it and evicts the node
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What happens if all of the nodes not able to access the voting disk?
This can be lead to split brain syndrome, each node acts as master node, with the disktimeout setting clusterware waits until that period can be delayed using disktimeout setting to reasonable value using crsctl. all nodes reboot.
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What happens if one of the node is not able to communicate via private interconnect?
Node OCSSD recognises it and evicts the node
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What happens if all of the nodes not able to communicate via private interconnect?
This can be lead to split brain syndrome, each node acts as master node, with the csstimeout setting clusterware waits until that period , can be delayed using csstimeout setting to reasonable value using crsctl. all nodes reboot.
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What is split brain syndrome?
Each node acts as master since there is communication or common storage access break down.
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Which background daemons initiates node eviction? ocssd ________________________________________
Which background daemon starts clusterware or the resources? crsd ________________________________________
Can you tell me under which user crs,cssd,oprocd, evmd, start and what is anything fails.
Process Functionality Failure of the Process Run as
CRSD Resource monitoring, failover, node recovery Restarts automatically, does not cause node restart root
OCSSD Basic node membership, Group Services, and Basic locking Node restart, evicts node oracle
EVMD Spawns child process event logger and generate callouts Automaitcally restarted does not cause reboot oracle
OPROCD Provides basic cluster integrity services, I/O fencing to disk Node restart root
Work Load Balancing & Failover questions:-
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What are my options for load balancing with Oracle RAC? Why do I get an uneven number of connections on my instances?
All the types of load balancing available currently (9i-10g) occur at connect time.
This means that it is very important how one balances connections and what these connections do on a long term basis.
Since establishing connections can be very expensive for your application, it is good programming practice to connect once and stay connected. This means one needs to be careful as to what option one uses. Oracle Net Services provides load balancing or you can use external methods such as hardware based or clusterware solutions.
The following options exist prior to Oracle RAC 10g Release 2 (for 10g Release 2 see Load Balancing Advisory):
Random
Either client side load balancing or hardware based methods will randomize the connections to the instances.
On the negative side this method is unaware of load on the connections or even if they are up meaning they might cause waits on TCP/IP timeouts.
Load Based
Server side load balancing (by the listener) redirects connections by default depending on the RunQ length of each of the instances. This is great for short lived connections. Terrible for persistent connections or login storms. Do not use this method for connections from connection pools or applicaton servers
Session Based
Server side load balancing can also be used to balance the number of connections to each instance. Session count balancing is method used when you set a listener parameter, prefer_least_loaded_node_listener-name=off. Note listener name is the actual name of the listener which is different on each node in your cluster and by default is listener_nodename.
Session based load balancing takes into account the number of sessions connected to each node and then distributes the connections to balance the number of sessions across the different nodes.
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How can a customer mask the change in their clustered database configuration from their client or application? (I.E. So I do not have to change the connection string when I add a node to the Oracle RAC database)
The combination of Server Side load balancing and Services allows you to easily mask cluster database configuration changes. As long as all instances register with all listeners (use the LOCAL_LISTENER and REMOTE_LISTENER parameters), server side load balancing will allow clients to connect to the service on currently available instances at connect time.
The load balancing advisory (setting a goal on the service) will give advice as to how many connections to send to each instance currently providing a service. When a service is enabled on an instance, as long as the instance registers with the listeners, the clients can start getting connections to the service and the load balancing advisory will include that instance is its advice.
With Oracle RAC 11g Release 2, the Single Client Access Name (SCAN) provides a single name to be put in the client connection string (as the address). Clients using SCAN never have to change even if the cluster configuration changes such as adding nodes.
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What is the Load Balancing Advisory?
To assist in the balancing of application workload across designated resources, Oracle Database 10g Release 2 provides the Load Balancing Advisory. This Advisory monitors the current workload activity across the cluster and for each instance where a service is active; it provides a percentage value of how much of the total workload should be sent to this instance as well as service quality flag. The feedback is provided as an entry in the Automatic Workload Repository and a FAN event is published. The easiest way for an application to take advantage of the load balancing advisory, is to enable Runtime Connection Load Balancing with an integrated client.
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How do I enable the load balancing advisory?
The load balancing advisory requires the use of services and Oracle Net connection load balancing.
To enable it, on the server: set a goal (service_time or throughput, and set CLB_GOAL=SHORT ) on your service.
For client, you must be using the connection pool.
For JDBC, enable the datasource parameter FastConnectionFailoverEnabled.
For ODP.NET enable the datasource parameter Load Balancing=true.
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Why do we have a Virtual IP (VIP) in Oracle RAC 10g or 11g? Why does it just return a dead connection when its primary node fails?
The goal is application availability.
When a node fails, the VIP associated with it is automatically failed over to some other node. When this occurs, the following things happen.
(1) VIP detects public network failure which generates a FAN event.
(2) the new node re-arps the world indicating a new MAC address for the IP.
(3) connected clients subscribing to FAN immediately receive ORA-3113 error or equivalent. Those not subscribing to FAN will eventually time out.
(4) New connection requests rapidly traverse the tnsnames.ora address list skipping over the dead nodes, instead of having to wait on TCP-IP timeouts
Without using VIPs or FAN, clients connected to a node that died will often wait for a TCP timeout period (which can be up to 10 min) before getting an error.
As a result, you don’t really have a good HA solution without using VIPs and FAN. The easiest way to use FAN is to use an integrated client with Fast Connection Failover (FCF) such as JDBC, OCI, or ODP.NET.
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What are my options for setting the Load Balancing Advisory GOAL on a Service?
The load balancing advisory is enabled by setting the GOAL on your service either through PL/SQL DBMS_SERVICE package or EM DBControl Clustered Database Services page. There are 3 options for GOAL:
None – Default setting, turn off advisory
THROUGHPUT – Work requests are directed based on throughput. This should be used when the work in a service completes at homogenous rates. An example is a trading system where work requests are similar lengths.
SERVICE_TIME – Work requests are directed based on response time. This should be used when the work in a service completes at various rates. An example is as internet shopping system where work requests are various lengths
Note: If using GOAL, you should set CLB_GOAL=SHORT

Model - 2
What is RAC?
RAC stands for Real Application cluster. It is a clustering solution from Oracle Corporation that ensures high availability of databases by providing instance failover, media failover features.

What is RAC and how is it different from non RAC databases?
RAC stands for Real Application Cluster, you have n number of instances running in their own separate nodes and based on the shared storage. Cluster is the key component and is a collection of servers operations as one unit. RAC is the best solution for high performance and high availably. Non RAC databases has single point of failure in case of hardware failure or server crash.
Give the usage of srvctl : srvctl start instance -d db_name -i "inst_name_list" [-o start_options] srvctl stop instance -d name -i "inst_name_list" [-o stop_options] srvctl stop instance -d orcl -i "orcl3,orcl4" -o immediate srvctl start database -d name [-o start_options] srvctl stop database -d name [-o stop_options] srvctl start database -d orcl -o mount
Mention the Oracle RAC software components :
Oracle RAC is composed of two or more database instances. They are composed of Memory structures and background processes same as the single instance database.Oracle RAC instances use two processes GES(Global Enqueue Service), GCS(Global Cache Service) that enable cache fusion.Oracle RAC instances are composed of following background processes:
ACMS—Atomic Controlfile to Memory Service (ACMS)
GTX0-j—Global Transaction Process
LMON—Global Enqueue Service Monitor
LMD—Global Enqueue Service Daemon
LMS—Global Cache Service Process
LCK0—Instance Enqueue Process
RMSn—Oracle RAC Management Processes (RMSn)
RSMN—Remote Slave Monitor

What is GRD?
GRD stands for Global Resource Directory. The GES and GCS maintains records of the statuses of each datafile and each cahed block using global resource directory.This process is referred to as cache fusion and helps in data integrity.
What are the different network components are in 10g RAC? public, private, and vip components
Private interfaces is for intra node communication. VIP is all about availability of application. When a node fails then the VIP component fail over to some other node, this is the reason that all applications should based on vip components means tns entries should have vip entry in the host list

Give Details on ACMS:
ACMS stands for Atomic Controlfile Memory Service.In an Oracle RAC environment ACMS is an agent that ensures a distributed SGA memory update(ie)SGA updates are globally committed on success or globally aborted in event of a failure.
What is Cache Fusion?
Cache fusion is the mechanism to transfer the data block from memory to memory of one node to the other.If two nodes require the same block for query or update, the block must be transfered from the cache of one node to the other. RAC system must equipped with low-latency and high speed inter-connect to make it happen.
Give Details on Cache Fusion:
Oracle RAC is composed of two or more instances. When a block of data is read from datafile by an instance within the cluster and another instance is in need of the same block,it is easy to get the block image from the insatnce which has the block in its SGA rather than reading from the disk. To enable inter instance communication Oracle RAC makes use of interconnects. The Global Enqueue Service(GES) monitors and Instance enqueue process manages the cahce fusion.
Cache Fusion is essentially a memory-to-memory transfer of data between the nodes in the RAC environment. Before Cache Fusion, a node was required to write some of the data to disk before it could be transferred to the next node in the cluster. Cache Fusion does a straight memory-to-memory transfer. In addition, each node's SGA has a map of what data is contained in the other node's data caches.
The performance improvement is phenomenal. Oracle leverages the vendor's high speed interconnects between the nodes to achieve the cache-to-cache data transfers. Before Cache Fusion, when you added a node to the cluster to increase performance of the application, it didn't always provide you with the performance improvement that you hoped for. With Cache Fusion, you can easily cost justify the addition of another node into a RAC cluster to increase the performance of the application running on it. Oracle sales pitches describe it as 'near linear horizontal scalability'.
What are the major RAC wait events?
In a RAC environment the buffer cache is global across all instances in the cluster and hence the processing differs.The most common wait events related to this are gc cr request and gc buffer busy

GC CR request :the time it takes to retrieve the data from the remote cache

Reason: RAC Traffic Using Slow Connection or Inefficient queries (poorly tuned queries will increase the amount of data blocks requested by an Oracle session. The more blocks requested typically means the more often a block will need to be read from a remote instance via the interconnect.)

GC BUFFER BUSY: It is the time the remote instance locally spends accessing the requested data block.

Give details on GTX0-j :
The process provides transparent support for XA global transactions in a RAC environment.The database autotunes the number of these processes based on the workload of XA global transactions.

Give details on LMON:
This process monitors global enques and resources across the cluster and performs global enqueue recovery operations.This is called as Global Enqueue Service Monitor.

Give details on LMD:
This process is called as global enqueue service daemon. This process manages incoming remote resource requests within each instance.

Give details on LMS:
This process is called as Global Cache service process.This process maintains statuses of datafiles and each cahed block by recording information in a Global Resource Dectory(GRD).This process also controls the flow of messages to remote instances and manages global data block access and transmits block images between the buffer caches of different instances.This processing is a part of cache fusion feature.

Give details on LCK0:
This process is called as Instance enqueue process.This process manages non-cache fusion resource requests such as libry and row cache requests.

Give details on RMSn:
This process is called as Oracle RAC management process.These pocesses perform managability tasks for Oracle RAC.Tasks include creation of resources related Oracle RAC when new instances are added to the cluster.

Give details on RSMN:
This process is called as Remote Slave Monitor.This process manages background slave process creation andd communication on remote instances. This is a background slave process.This process performs tasks on behalf of a co-ordinating process running in another instance.

What components in RAC must reside in shared storage?
All datafiles, controlfiles, SPFIles, redo log files must reside on cluster-aware shred storage.

What is the significance of using cluster-aware shared storage in an Oracle RAC environment?
All instances of an Oracle RAC can access all the datafiles,control files, SPFILE's, redolog files when these files are hosted out of cluster-aware shared storage which are group of shared disks.

Give few examples for solutions that support cluster storage:
ASM(automatic storage management),raw disk devices,network file system(NFS), OCFS2 and OCFS(Oracle Cluster Fie systems).

What is an interconnect network?
An interconnect network is a private network that connects all of the servers in a cluster. The interconnect network uses a switch/multiple switches that only the nodes in the cluster can access.

How can we configure the cluster interconnect?
Configure User Datagram Protocol(UDP) on Gigabit ethernet for cluster interconnect.On unix and linux systems we use UDP and RDS(Reliable data socket) protocols to be used by Oracle Clusterware.Windows clusters use the TCP protocol.

Can we use crossover cables with Oracle Clusterware interconnects?
No, crossover cables are not supported with Oracle Clusterware intercnects.

What is the use of cluster interconnect?
Cluster interconnect is used by the Cache fusion for inter instance communication.

How do users connect to database in an Oracle RAC environment?
Users can access a RAC database using a client/server configuration or through one or more middle tiers ,with or without connection pooling.Users can use oracle services feature to connect to database.

What is the use of a service in Oracle RAC environment?
Applications should use the services feature to connect to the Oracle database.Services enable us to define rules and characteristics to control how users and applications connect to database instances.

What are the characteristics controlled by Oracle services feature?
The charateristics include a unique name, workload balancing and failover options,and high availability characteristics.
What enables the load balancing of applications in RAC?
Oracle Net Services enable the load balancing of application connections across all of the instances in an Oracle RAC database.

What is a virtual IP address or VIP?
A virtl IP address or VIP is an alternate IP address that the client connectins use instead of the standard public IP address. To configureVIP address, we need to reserve a spare IP address for each node, and the IP addresses must use the same subnet as the public network.

What is the use of VIP?
If a node fails, then the node's VIP address fails over to another node on which the VIP address can accept TCP connections but it cannot accept Oracle connections.

Give situations under which VIP address failover happens:
VIP addresses failover happens when the node on which the VIP address runs fails, all interfaces for the VIP address fails,all interfaces for the VIP address are disconnected from the network.

What is the significance of VIP address failover?
When a VIP address failover happens, Clients that attempt to connect to the VIP address receive a rapid connection refused error .They don't have to wait for TCP connection timeout messages.

What are the administrative tools used for Oracle RAC environments?
Oracle RAC cluster can be administered as a single image using OEM(Enterprise Manager),SQL*PLUS,Servercontrol(SRVCTL),clusterverificationutility(cvu),DBCA,NETCA

How do we verify that RAC instances are running?
Issue the following query from any one node connecting through SQL*PLUS.
$connect sys/sys as sysdba
SQL>select * from V$ACTIVE_INSTANCES;
The query gives the instance number under INST_NUMBER column,host_:instancename under INST_NAME column.

What is FAN?
Fast application Notification as it abbreviates to FAN relates to the events related to instances,services and nodes.This is a notification mechanism that Oracle RAc uses to notify other processes about the configuration and service level information that includes service status changes such as,UP or DOWN events.Applications can respond to FAN events and take immediate action.

Where can we apply FAN UP and DOWN events?
FAN UP and FAN DOWN events can be applied to instances,services and nodes.
State the use of FAN events in case of a cluster configuration change?
During times of cluster configuration changes,Oracle RAC high availability framework publishes a FAN event immediately when a state change occurs in the cluster.So applications can receive FAN events and react immediately.This prevents applications from polling database and detecting a problem after such a state change.

Why should we have seperate homes for ASm instance?
It is a good practice to have ASM home seperate from the database hom(ORACLE_HOME).This helps in upgrading and patching ASM and the Oracle database software independent of each other.Also,we can deinstall the Oracle database software independent of the ASM instance.

What is the advantage of using ASM?
Having ASM is the Oracle recommended storage option for RAC databases as the ASM maximizes performance by managing the storage configuration across the disks.ASM does this by distributing the database file across all of the available storage within our cluster database environment.

What is rolling upgrade?
It is a new ASM feature from Database 11g.ASM instances in Oracle database 11g release(from 11.1) can be upgraded or patched using rolling upgrade feature. This enables us to patch or upgrade ASM nodes in a clustered environment without affecting database availability.During a rolling upgrade we can maintain a functional cluster while one or more of the nodes in the cluster are running in different software versions.

Can rolling upgrade be used to upgrade from 10g to 11g database?
No,it can be used only for Oracle database 11g releases(from 11.1).

State the initialization parameters that must have same value for every instance in an Oracle RAC database:
Some initialization parameters are critical at the database creation time and must have same values.Their value must be specified in SPFILE or PFILE for every instance.The list of parameters that must be identical on every instance are given below:
ACTIVE_INSTANCE_COUNT
ARCHIVE_LAG_TARGET
COMPATIBLE
CLUSTER_DATABASE
CLUSTER_DATABASE_INSTANCE
CONTROL_FILES
DB_BLOCK_SIZE
DB_DOMAIN
DB_FILES
DB_NAME
DB_RECOVERY_FILE_DEST
DB_RECOVERY_FILE_DEST_SIZE
DB_UNIQUE_NAME
INSTANCE_TYPE (RDBMS or ASM)
PARALLEL_MAX_SERVERS
REMOTE_LOGIN_PASSWORD_FILE
UNDO_MANAGEMENT
What is ORA-00603: ORACLE server session terminated by fatal error or ORA-29702: error occurred in Cluster Group Service operation?
RAC node name was listed in the loopback address...

Can the DML_LOCKS and RESULT_CACHE_MAX_SIZE be identical on all instances?
These parameters can be identical on all instances only if these parameter values are set to zero.
What two parameters must be set at the time of starting up an ASM instance in a RAC environment?The parameters CLUSTER_DATABASE and INSTANCE_TYPE must be set.

Mention the components of Oracle clusterware:
Oracle clusterware is made up of components like voting disk and Oracle Cluster Registry(OCR).
What is a CRS resource?
Oracle clusterware is used to manage high-availability operations in a cluster.Anything that Oracle Clusterware manages is known as a CRS resource.Some examples of CRS resources are database,an instance,a service,a listener,a VIP address,an application process etc.

What is the use of OCR?
Oracle clusterware manages CRS resources based on the configuration information of CRS resources stored in OCR(Oracle Cluster Registry).

How does a Oracle Clusterware manage CRS resources?
Oracle clusterware manages CRS resources based on the configuration information of CRS resources stored in OCR(Oracle Cluster Registry).

Name some Oracle clusterware tools and their uses?
OIFCFG - allocating and deallocating network interfaces
OCRCONFIG - Command-line tool for managing Oracle Cluster Registry
OCRDUMP - Identify the interconnect being used
CVU - Cluster verification utility to get status of CRS resources

What are the modes of deleting instances from ORacle Real Application cluster Databases?
We can delete instances using silent mode or interactive mode using DBCA(Database Configuration Assistant).

How do we remove ASM from a Oracle RAC environment?
We need to stop and delete the instance in the node first in interactive or silent mode.After that asm can be removed using srvctl tool as follows: srvctl stop asm -n node_name srvctl remove asm -n node_name
We can verify if ASM has been removed by issuing the following command: srvctl config asm -n node_name

How do we verify that an instance has been removed from OCR after deleting an instance?
Issue the following srvctl command: srvctl config database -d database_name cd CRS_HOME/bin
./crs_stat

How do we verify an existing current backup of OCR?
We can verify the current backup of OCR using the following command : ocrconfig -showbackup
What are the performance views in an Oracle RAC environment?
We have v$ views that are instance specific. In addition we have GV$ views called as global views that has an INST_ID column of numeric data type.GV$ views obtain information from individual V$ views.
What are the types of connection load-balancing?
There are two types of connection load-balancing:server-side load balancing and client-side load balancing.

What is the difference between server-side and client-side connection load balancing?
Client-side balancing happens at client side where load balancing is done using listener.In case of server-side load balancing listener uses a load-balancing advisory to redirect connections to the instance providing best service.

What are the three greatest benefits that RAC provides?
The three main benefits are availability, scalability, and the ability to use low cost commodity hardware. RAC allows an application to scale vertically, by adding CPU, disk and memory resources to an individual server. But RAC also provides horizontal scalability, which is achieved by adding new nodes into the cluster. RAC also allows an organization to bring these resources online as they are needed. This can save a small or midsize organization a lot of money in the early stages of a project.
In a RAC environment, if a node in the cluster fails, the application continues to run on the surviving nodes contained in the cluster. If your application is configured correctly, most users won't even know that the node they were running on became unavailable.

What are the major RAC wait events?
In a RAC environment the buffer cache is global across all instances in the cluster and hence the processing differs.The most common wait events related to this are gc cr request and gc buffer busy

GC CR request: the time it takes to retrieve the data from the remote cache

Reason: RAC Traffic Using Slow Connection or Inefficient queries (poorly tuned queries will increase the amount of data blocks requested by an Oracle session. The more blocks requested typically means the more often a block will need to be read from a remote instance via the interconnect.)
GC BUFFER BUSY: It is the time the remote instance locally spends accessing the requested data block.

What are the different network components in Oracle 10g RAC?
We have public, private, and VIP components. Private interfaces is for intra node communication. VIP is all about availability of application. When a node fails then the VIP component will fail over to some other node, this is the reason that all applications should be based on VIP components. This means that tns entries should have VIP entry in the host list.
Model – 3
Q What is SCAN?

Single Client Access Name (SCAN) is s a new Oracle Real Application Clusters (RAC) 11g Release 2 feature that provides a single name for clients to access an Oracle Database running in a cluster. The benefit is clients using SCAN do not need to change if you add or remove nodes in the cluster.

________________________________________
Q what is dynamic remastering ? When will the dynamic remastering happens? dynamic remastering is ability to move the ownership of resource from one instance to another instance in RAC. dynamic resource remastering is used to implement for resource affinity for increased performance. resource affinity optimized the system in situation where update transactions are being executed in one instance. when activity shift to another instance the resource affinity correspondingly move to another instance. If activity is not localized then resource ownership is hashed to the instance.

In 10g dynamic remastering happens in file+object level.the process of remastering is very stringent. For one instance should touch more than 50 times than the other instance in particular period(say 10 mints). this touch ratio and time can be tuned by gc_affinity_limit and _gc_affinity_time parameter.

________________________________________
Q why we required to maintain odd number of voting disks?
Odd number of disk are to avoid split brain, When Nodes in cluster can't talk to each other they run to lock the Voting disk and whoever lock the more disk will survive, if disk number are even there are chances that node might lock 50% of disk (2 out of 4) then how to decide which node to evict. whereas when number is odd, one will be higher than other and each for cluster to evict the node with less number

________________________________________
Q How you check the health of Your RAC Database? 'crsctl' command from root or oracle user can be used to check the clusterware health But for starting or stopping we have to use root user or any privilege user.

[oracle@TEST_NODE1 ~]$ crsctl check crs
CSS appears healthy
CRS appears healthy
EVM appears healthy

________________________________________
Q How you check the services in RAC Node? We can check the service or start the services with 'srvctl' command.load balanced/TAF service named RAC online.

[oracle@TEST_NODE1 ~]$ srvctl start service -d orcl -s RAC
[oracle@TEST_NODE1 ~]$ crsstat

________________________________________
Q If there is some issue with virtual IP how will you troubleshoot it?How will you change virtual ip? To change the VIP (virtual IP) on a RAC node, use the command

[oracle@testnode oracle]$ srvctl modify nodeapps -A new_address

________________________________________
Q How you will backup your RAC Database? Backup strategy of RAC Database:
An RAC Database consists of
1)OCR
2)Voting disk &
3)Database files, controlfiles, redolog files & Archive log files

________________________________________
Q Do you have any idea of load balancing in application?How load balancing is done? http://practicalappsdba.wordpress.com/category/for-master-apps-dbas/ ________________________________________
Q What is RAC?
RAC stands for Real Application cluster. It is a clustering solution from Oracle Corporation that ensures high availability of databases by providing instance failover, media failover features.

________________________________________
Q What is RAC and how is it different from non RAC databases?
RAC stands for Real Application Cluster, you have n number of instances running in their own separate nodes and based on the shared storage. Cluster is the key component and is a collection of servers operations as one unit. RAC is the best solution for high performance and high availably. Non RAC databases has single point of failure in case of hardware failure or server crash.

________________________________________
Q Give the usage of srvctl ? srvctl start instance -d db_name -i "inst_name_list" [-o start_options] srvctl stop instance -d name -i "inst_name_list" [-o stop_options] srvctl stop instance -d orcl -i "orcl3,orcl4" -o immediate srvctl start database -d name [-o start_options] srvctl stop database -d name [-o stop_options] srvctl start database -d orcl -o mount

________________________________________
Q Mention the Oracle RAC software components ?
Oracle RAC is composed of two or more database instances. They are composed of Memory structures and background processes same as the single instance database.Oracle RAC instances use two processes GES(Global Enqueue Service), GCS(Global Cache Service) that enable cache fusion.Oracle RAC instances are composed of following background processes:
ACMS—Atomic Controlfile to Memory Service (ACMS)
GTX0-j—Global Transaction Process
LMON—Global Enqueue Service Monitor
LMD—Global Enqueue Service Daemon
LMS—Global Cache Service Process
LCK0—Instance Enqueue Process
RMSn—Oracle RAC Management Processes (RMSn)
RSMN—Remote Slave Monitor

________________________________________

Q What is GRD?
GRD stands for Global Resource Directory. The GES and GCS maintains records of the statuses of each datafile and each cahed block using global resource directory.This process is referred to as cache fusion and helps in data integrity.

________________________________________
Q What are the different network components are in 10g RAC? public, private, and vip components
Private interfaces is for intra node communication. VIP is all about availability of application. When a node fails then the VIP component fail over to some other node, this is the reason that all applications should based on vip components means tns entries should have vip entry in the host list

________________________________________

Q Give Details on ACMS:
ACMS stands for Atomic Controlfile Memory Service.In an Oracle RAC environment ACMS is an agent that ensures a distributed SGA memory update(ie)SGA updates are globally committed on success or globally aborted in event of a failure.

________________________________________
Q What are the major RAC wait events?
In a RAC environment the buffer cache is global across all instances in the cluster and hence the processing differs.The most common wait events related to this are gc cr request and gc buffer busy

GC CR request :the time it takes to retrieve the data from the remote cache

Reason: RAC Traffic Using Slow Connection or Inefficient queries (poorly tuned queries will increase the amount of data blocks requested by an Oracle session. The more blocks requested typically means the more often a block will need to be read from a remote instance via the interconnect.)

GC BUFFER BUSY: It is the time the remote instance locally spends accessing the requested data block.

________________________________________

Q Give details on GTX0-j
The process provides transparent support for XA global transactions in a RAC environment.The database autotunes the number of these processes based on the workload of XA global transactions.

________________________________________

Q Give details on LMON
This process monitors global enques and resources across the cluster and performs global enqueue recovery operations.This is called as Global Enqueue Service Monitor.

________________________________________

Q Give details on LMD
This process is called as global enqueue service daemon. This process manages incoming remote resource requests within each instance.

________________________________________

Q Give details on LMS
This process is called as Global Cache service process.This process maintains statuses of datafiles and each cahed block by recording information in a Global Resource Dectory(GRD).This process also controls the flow of messages to remote instances and manages global data block access and transmits block images between the buffer caches of different instances.This processing is a part of cache fusion feature.

________________________________________

Q Give details on LCK0
This process is called as Instance enqueue process.This process manages non-cache fusion resource requests such as libry and row cache requests.

________________________________________

Q Give details on RMSn
This process is called as Oracle RAC management process.These pocesses perform managability tasks for Oracle RAC.Tasks include creation of resources related Oracle RAC when new instances are added to the cluster.

________________________________________
Q How to export and import crs resources while migrating Oracle RAC to new server.
Below script generate svrctl add script for database, instance, service and 11G listeners from OCR from current RAC.
Save the result of the script and run it at new RAC.

for DBNAME in $(srvctl config database) do # Generate DB resource

srvctl config database -d $DBNAME -a | awk -v dbname="$DBNAME" \
'BEGIN { FS=":" }
$1~/Oracle home/ || $1~/ORACLE_HOME/ {dbhome = "-o" $2}
$1~/Spfile/ || $1~/SPFILE/ {spfile = "-p" $2}
$1~/Disk Groups/ {dg = "-a" $2}
END { if (avail == "-a ") {avail = ""}; printf "%s %s %s %s %s\n", "srvctl add database -d ", dbname, dbhome, spfile, dg }'

# Generate Instance resource

srvctl status database -d $DBNAME | awk -v dbname="$DBNAME" \
'$4~/running/ { printf "%s %s %s %s %s %s\n", "srvctl add instance -d ",dbname, " -i ", $2 ," -n ", $7 }
$5~/running/ { printf "%s %s %s %s %s %s \n", "srvctl add instance -d ",dbname, " -i ", $2 ," -n ", $8 }'

# Modify instance for 10G - ASM dependency

if [ $(echo $ORACLE_HOME | grep "1020" | wc -l ) -eq 1 ] then srvctl status database -d $DBNAME | awk -v dbname="$DBNAME" \
'$2~/1$/ { printf "%s %s %s %s %s \n", "srvctl modify instance -d ",dbname, " -i ", $2 ," -s +ASM1" }
$2~/2$/ { printf "%s %s %s %s %s \n", "srvctl modify instance -d ",dbname, " -i ", $2 ," -s +ASM2" }
$2~/3$/ { printf "%s %s %s %s %s \n", "srvctl modify instance -d ",dbname, " -i ", $2 ," -s +ASM3" }
$2~/4$/ { printf "%s %s %s %s %s \n", "srvctl modify instance -d ",dbname, " -i ", $2 ," -s +ASM4" }' fi echo "srvctl start database -d $DBNAME"

# Generate Service resource

snamelist=$(srvctl status service -d $DBNAME | awk '{print $2}')

for sname in $snamelist do srvctl config service -d $DBNAME -s $sname| awk -v dbname="$DBNAME" -v sname=$sname \
'BEGIN { FS=":"}
$1~/Preferred instances/ {pref = "-r" $2}
$1~/PREF/ {pref = "-r" $2; sub(/AVAIL/, "", pref) }
$1~/Available instances/ {avail = "-a" $2}
$2~/AVAIL/ {avail = "-a" $3}
$1~/Failover type/ {ft = "-e" $2}
$1~/Failover method/ {fm = "-m" $2}
$1~/Runtime Load Balancing Goal/ {g = "-B" $2}
END { if (avail == "-a ") {avail = ""}; printf "%s %s %s %s %s %s %s %s %s %s\n", "srvctl add service -d ",dbname, "-s ", sname, pref, avail ,ft, fm,g, "-P BASIC"}' echo "srvctl start service -d $DBNAME -s $sname" done done

# Listener at 11G Home. 10G listener can't ba added with srvctl.

srvctl config listener | awk \
'BEGIN { FS=":"; state = 0; }
$1~/Name/ {lname = "-l" $2; state=1};
$1~/Home/ && state == 1 {ohome = "-o" $2; state=2;}
$1~/End points/ && state == 2 {lport = "-p " $3; state=3;} state == 3 {if (ohome != "-o ") {printf "%s %s %s %s\n", "srvctl add listener ", lname, ohome, lport;} state=0;}'

________________________________________ Q Give details on RSMN
This process is called as Remote Slave Monitor.This process manages background slave process creation andd communication on remote instances. This is a background slave process.This process performs tasks on behalf of a co-ordinating process running in another instance.

________________________________________
Q What components in RAC must reside in shared storage?
All datafiles, controlfiles, SPFIles, redo log files must reside on cluster-aware shred storage.

________________________________________

Q What is the significance of using cluster-aware shared storage in an Oracle RAC environment?
All instances of an Oracle RAC can access all the datafiles,control files, SPFILE's, redolog files when these files are hosted out of cluster-aware shared storage which are group of shared disks.

________________________________________

Q Give few examples for solutions that support cluster storage
ASM(automatic storage management),raw disk devices,network file system(NFS), OCFS2 and OCFS(Oracle Cluster Fie systems).

________________________________________

Q What is an interconnect network?
An interconnect network is a private network that connects all of the servers in a cluster. The interconnect network uses a switch/multiple switches that only the nodes in the cluster can access.

________________________________________

Q How can we configure the cluster interconnect?
Configure User Datagram Protocol(UDP) on Gigabit ethernet for cluster interconnect.On unix and linux systems we use UDP and RDS(Reliable data socket) protocols to be used by Oracle Clusterware.Windows clusters use the TCP protocol.

________________________________________

Q Can we use crossover cables with Oracle Clusterware interconnects?
No, crossover cables are not supported with Oracle Clusterware intercnects.

________________________________________

Q What is the use of cluster interconnect?
Cluster interconnect is used by the Cache fusion for inter instance communication.

________________________________________

Q How do users connect to database in an Oracle RAC environment?
Users can access a RAC database using a client/server configuration or through one or more middle tiers ,with or without connection pooling.Users can use oracle services feature to connect to database.

________________________________________

Q What is the use of a service in Oracle RAC environment?
Applications should use the services feature to connect to the Oracle database.Services enable us to define rules and characteristics to control how users and applications connect to database instances.

________________________________________

Q What are the characteristics controlled by Oracle services feature?
The charateristics include a unique name, workload balancing and failover options,and high availability characteristics.

________________________________________
Q What enables the load balancing of applications in RAC?
Oracle Net Services enable the load balancing of application connections across all of the instances in an Oracle RAC database.

________________________________________

Q What is a virtual IP address or VIP?
A virtl IP address or VIP is an alternate IP address that the client connectins use instead of the standard public IP address. To configureVIP address, we need to reserve a spare IP address for each node, and the IP addresses must use the same subnet as the public network.

________________________________________

Q What is the use of VIP?
If a node fails, then the node's VIP address fails over to another node on which the VIP address can accept TCP connections but it cannot accept Oracle connections.

________________________________________

Q Give situations under which VIP address failover happens
VIP addresses failover happens when the node on which the VIP address runs fails, all interfaces for the VIP address fails, all interfaces for the VIP address are disconnected from the network.

________________________________________

Q What is the significance of VIP address failover?
When a VIP address failover happens, Clients that attempt to connect to the VIP address receive a rapid connection refused error .They don't have to wait for TCP connection timeout messages.

________________________________________

Q What are the administrative tools used for Oracle RAC environments?
Oracle RAC cluster can be administered as a single image using OEM(Enterprise Manager),SQL*PLUS,Servercontrol(SRVCTL),clusterverificationutility(cvu),DBCA,NETCA

________________________________________

Q How do we verify that RAC instances are running?
Issue the following query from any one node connecting through SQL*PLUS.
$connect sys/sys as sysdba
SQL>select * from V$ACTIVE_INSTANCES;
The query gives the instance number under INST_NUMBER column,host_:instancename under INST_NAME column.

________________________________________

Q What is FAN?
Fast application Notification as it abbreviates to FAN relates to the events related to instances,services and nodes.This is a notification mechanism that Oracle RAc uses to notify other processes about the configuration and service level information that includes service status changes such as,UP or DOWN events.Applications can respond to FAN events and take immediate action.

________________________________________

Q Where can we apply FAN UP and DOWN events?
FAN UP and FAN DOWN events can be applied to instances,services and nodes.
State the use of FAN events in case of a cluster configuration change?
During times of cluster configuration changes,Oracle RAC high availability framework publishes a FAN event immediately when a state change occurs in the cluster.So applications can receive FAN events and react immediately.This prevents applications from polling database and detecting a problem after such a state change.

________________________________________

Q Why should we have seperate homes for ASm instance?
It is a good practice to have ASM home seperate from the database hom(ORACLE_HOME).This helps in upgrading and patching ASM and the Oracle database software independent of each other.Also,we can deinstall the Oracle database software independent of the ASM instance.

________________________________________

Q What is the advantage of using ASM?
Having ASM is the Oracle recommended storage option for RAC databases as the ASM maximizes performance by managing the storage configuration across the disks.ASM does this by distributing the database file across all of the available storage within our cluster database environment.

________________________________________

Q What is rolling upgrade?
It is a new ASM feature from Database 11g.ASM instances in Oracle database 11g release(from 11.1) can be upgraded or patched using rolling upgrade feature. This enables us to patch or upgrade ASM nodes in a clustered environment without affecting database availability.During a rolling upgrade we can maintain a functional cluster while one or more of the nodes in the cluster are running in different software versions.

________________________________________

Q Can rolling upgrade be used to upgrade from 10g to 11g database?
No,it can be used only for Oracle database 11g releases(from 11.1).

________________________________________

Q State the initialization parameters that must have same value for every instance in an Oracle RAC database
Some initialization parameters are critical at the database creation time and must have same values.Their value must be specified in SPFILE or PFILE for every instance.The list of parameters that must be identical on every instance are given below:
ACTIVE_INSTANCE_COUNT
ARCHIVE_LAG_TARGET
COMPATIBLE
CLUSTER_DATABASE
CLUSTER_DATABASE_INSTANCE
CONTROL_FILES
DB_BLOCK_SIZE
DB_DOMAIN
DB_FILES
DB_NAME
DB_RECOVERY_FILE_DEST
DB_RECOVERY_FILE_DEST_SIZE
DB_UNIQUE_NAME
INSTANCE_TYPE (RDBMS or ASM)
PARALLEL_MAX_SERVERS
REMOTE_LOGIN_passWORD_FILE
UNDO_MANAGEMENT

________________________________________
Q What is ORA-00603: ORACLE server session terminated by fatal error or ORA-29702: error occurred in Cluster Group Service operation?
RAC node name was listed in the loopback address...

________________________________________

Q Can the DML_LOCKS and RESULT_CACHE_MAX_SIZE be identical on all instances?
These parameters can be identical on all instances only if these parameter values are set to zero.
What two parameters must be set at the time of starting up an ASM instance in a RAC environment?The parameters CLUSTER_DATABASE and INSTANCE_TYPE must be set.

________________________________________

Q Mention the components of Oracle clusterware
Oracle clusterware is made up of components like voting disk and Oracle Cluster Registry(OCR).

________________________________________
Q What is a CRS resource?
Oracle clusterware is used to manage high-availability operations in a cluster.Anything that Oracle Clusterware manages is known as a CRS resource.Some examples of CRS resources are database,an instance,a service,a listener,a VIP address,an application process etc.

________________________________________

Q What is the use of OCR?
Oracle clusterware manages CRS resources based on the configuration information of CRS resources stored in OCR(Oracle Cluster Registry).

________________________________________

Q How does a Oracle Clusterware manage CRS resources?
Oracle clusterware manages CRS resources based on the configuration information of CRS resources stored in OCR(Oracle Cluster Registry).

________________________________________

Q Name some Oracle clusterware tools and their uses?
OIFCFG - allocating and deallocating network interfaces
OCRCONFIG - Command-line tool for managing Oracle Cluster Registry
OCRDUMP - Identify the interconnect being used
CVU - Cluster verification utility to get status of CRS resources

________________________________________

Q What are the modes of deleting instances from ORacle Real Application cluster Databases?
We can delete instances using silent mode or interactive mode using DBCA(Database Configuration Assistant).

________________________________________

Q How do we remove ASM from a Oracle RAC environment?
We need to stop and delete the instance in the node first in interactive or silent mode.After that asm can be removed using srvctl tool as follows: srvctl stop asm -n node_name srvctl remove asm -n node_name
We can verify if ASM has been removed by issuing the following command: srvctl config asm -n node_name

________________________________________

Q How do we verify that an instance has been removed from OCR after deleting an instance?
Issue the following srvctl command: srvctl config database -d database_name cd CRS_HOME/bin
./crs_stat

________________________________________

Q How do we verify an existing current backup of OCR?
We can verify the current backup of OCR using the following command : ocrconfig -showbackup
What are the performance views in an Oracle RAC environment?
We have v$ views that are instance specific. In addition we have GV$ views called as global views that has an INST_ID column of numeric data type.GV$ views obtain information from individual V$ views.
What are the types of connection load-balancing?
There are two types of connection load-balancing:server-side load balancing and client-side load balancing.

________________________________________

Q What is the difference between server-side and client-side connection load balancing?
Client-side balancing happens at client side where load balancing is done using listener.In case of server-side load balancing listener uses a load-balancing advisory to redirect connections to the instance providing best service.

________________________________________

Q What are the three greatest benefits that RAC provides??
The three main benefits are availability, scalability, and the ability to use low cost commodity hardware. RAC allows an application to scale vertically, by adding CPU, disk and memory resources to an individual server. But RAC also provides horizontal scalability, which is achieved by adding new nodes into the cluster. RAC also allows an organization to bring these resources online as they are needed. This can save a small or midsize organization a lot of money in the early stages of a project.
In a RAC environment, if a node in the cluster fails, the application continues to run on the surviving nodes contained in the cluster. If your application is configured correctly, most users won't even know that the node they were running on became unavailable.

________________________________________
Q What are the major RAC wait events?
In a RAC environment the buffer cache is global across all instances in the cluster and hence the processing differs.The most common wait events related to this are gc cr request and gc buffer busy

GC CR request: the time it takes to retrieve the data from the remote cache

Reason: RAC Traffic Using Slow Connection or Inefficient queries (poorly tuned queries will increase the amount of data blocks requested by an Oracle session. The more blocks requested typically means the more often a block will need to be read from a remote instance via the interconnect.)
GC BUFFER BUSY: It is the time the remote instance locally spends accessing the requested data block.

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Q What are the different network components in Oracle 10g RAC?

We have public, private, and VIP components. Private interfaces is for intra node communication. VIP is all about availability of application. When a node fails then the VIP component will fail over to some other node, this is the reason that all applications should be based on VIP components. This means that tns entries should have VIP entry in the host list.

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Q Tune the following RAC DATABASE (DBNAME=PROD) which is 3 node RAC.

PROD1 PROD2 PROD3
CPU 8 CPU 15 CPU 8
32 GB RAM 12 GB RAM 16 GB RAM

What are you looking for here? What tuning information do you expect?
It is a 3 node cluster with different hardware configuration running RAC.
I would put 20% of the memory for Oracle in each node. So that would mean that the SGA is different in each of the nodes.
Also since the CPU's are different PROD2 can have more number of max number of processes as compared to the rest of them.

But as I said this is just configuration, this is not tuning. Question is not clear.

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Q Write a sample script for RMAN for the recovery if all the instance are down.(First explain the procedure how you will restore)
Bring all nodes down.
Start one Node
Restore all datafiles and archive logs.
Recover 1 Node.
Open the database. bring other nodes up.
Confirm that all nodes are operational.

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Q. Clients are performing some operation and suddenly one of the datafile is experiencing problem what do you do? The cluster is a two node one.
A. Bring the datafile offline recover the datafile.

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Q. How can you connect to a specific node in a RAC environment?
A. tnsnames.ora ensure that you have INSTANCE_NAME specified in it.

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Q How to move OCR and Voting disk to new storage device?
Moving OCR
==========
You must be logged in as the root user, because root owns the OCR files. Also an ocrmirror must be in place before trying to replace the OCR device.

Make sure there is a recent backup of the OCR file before making any changes:

ocrconfig –showbackup

If there is not a recent backup copy of the OCR file, an export can be taken for the current OCR file. Use the following command to generate an export of the online OCR file:

In 10.2

# ocrconfig –export -s online

In 11g

# ocrconfig -manualbackup

The new OCR disk must be owned by root, must be in the oinstall group, and must have permissions set to 640. Provide at least 100 MB disk space for the OCR.

On one node as root run:

# ocrconfig -replace ocr
# ocrconfig -replace ocrmirror

Now run ocrcheck to verify if the OCR is pointing to the new file

Moving Voting Disk
==================

Note: crsctl votedisk commands must be run as root

Shutdown the Oracle Clusterware (crsctl stop crs as root) on all nodes before making any modification to the voting disk. Determine the current voting disk location using:

crsctl query css votedisk

Take a backup of all voting disk:

dd if=voting_disk_name of=backup_file_name

To move a Voting Disk, provide the full path including file name:

crsctl delete css votedisk –force crsctl add css votedisk –force

After modifying the voting disk, start the Oracle Clusterware stack on all nodes

# crsctl start crs

Verify the voting disk location using

crsctl query css votedisk

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Q What is runfixup.sh script in Oracle Clusterware 11g release 2 installation
With Oracle Clusterware 11g release 2, Oracle Universal Installer (OUI) detects when the minimum requirements for an installation are not met, and creates shell scripts, called fixup scripts, to finish incomplete system configuration steps. If OUI detects an incomplete task, then it generates fixup scripts (runfixup.sh). You can run the fixup script after you click the Fix and Check Again Button.
The Fixup script does the following:
■ If necessary sets kernel parameters to values required for successful installation, including: – Shared memory parameters.
– Open file descriptor and UDP send/receive parameters.
■ Sets permissions on the Oracle Inventory (central inventory) directory.
■ Reconfigures primary and secondary group memberships for the installation owner, if necessary, for the Oracle Inventory directory and the operating system privileges groups.
■ Sets shell limits if necessary to required values.

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Q When exactly during the installation process are clusterware components created?

After fulfilling the pre-installation requirements, the basic installation steps to follow are:

1. Invoke the Oracle Universal Installer (OUI)

2. Enter the different information for some components like:
- name of the cluster
- public and private node names
- location for OCR and Voting Disks
- network interfaces used for RAC instances
-etc.

3. After the Summary screen, OUI will start copying under the $CRS_HOME (this is the $ORACLE_HOME for Oracle Clusterware) in the local node the libraries and executables.
- here we will have the daemons and scripts init.* created and configured properly.

Oracle Clusterware is formed of several daemons, each one of which have a special function inside the stack. Daemons are executed via the init.* scripts (init.cssd, init.crsd and init.evmd).

- note that for CRS only some client libraries are recreated, but not all the executables (as for the RDBMS).

4. Later the software is propagated to the rest of the nodes in the cluster and the oraInventory is updated.

5. The installer will ask to execute root.sh on each node. Until this step the software for Oracle Clusterware is inside the $CRS_HOME.

Running root.sh will create several components outside the $CRS_HOME:

- OCR and VD will be formated.

- control files (or SCLS_SRC files ) will be created with the correct contents to start Oracle Clusterware.

These files are used to control some aspects of Oracle Clusterware like:
- enable/disable processes from the CSSD family (Eg. oprocd, oslsvmon)
- stop the daemons (ocssd.bin, crsd.bin, etc).
- prevent Oracle Clusterware from being started when the machine boots.
- etc.

- /etc/inittab will be updated and the init process is notified.

In order to start the Oracle Clusterware daemons, the init.* scripts first need to be run. These scripts are executed by the daemon init. To accomplish this some entries must be created in the file /etc/inittab.

- the different processes init.* (init.cssd, init.crsd, etc) will start the daemons (ocssd.bin, crsd.bin, etc). When all the daemons are running then we can say that the installation was successful

- On 10.2 and later, running root.sh on the last node in the cluster also will create the nodeapps (VIP, GSD and ONS). On 10.1, VIPCA is executed as part of the RAC installation.

6. After running root.sh on each node, we need to continue with the OUI session. After pressing the 'OK' button OUI will include the information for the public and cluster_interconnect interfaces. Also CVU (Cluster Verification Utility) will be executed.

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Q What are Oracle Clusterware processes for 10g on Unix and Linux

Cluster Synchronization Services (ocssd) — Manages cluster node membership and runs as the oracle user; failure of this process results in cluster restart.

Cluster Ready Services (crsd) — The crs process manages cluster resources (which could be a database, an instance, a service, a Listener, a virtual IP (VIP) address, an application process, and so on) based on the resource's configuration information that is stored in the OCR. This includes start, stop, monitor and failover operations. This process runs as the root user

Event manager daemon (evmd) —A background process that publishes events that crs creates.

Process Monitor Daemon (OPROCD) —This process monitor the cluster and provide I/O fencing. OPROCD performs its check, stops running, and if the wake up is beyond the expected time, then OPROCD resets the processor and reboots the node. An OPROCD failure results in Oracle Clusterware restarting the node. OPROCD uses the hangcheck timer on Linux platforms.

RACG (racgmain, racgimon) —Extends clusterware to support Oracle-specific requirements and complex resources. Runs server callout scripts when FAN events occur.

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Q What are Oracle database background processes specific to RAC

•LMS—Global Cache Service Process

•LMD—Global Enqueue Service Daemon

•LMON—Global Enqueue Service Monitor

•LCK0—Instance Enqueue Process

To ensure that each Oracle RAC database instance obtains the block that it needs to satisfy a query or transaction, Oracle RAC instances use two processes, the Global Cache Service (GCS) and the Global Enqueue Service (GES). The GCS and GES maintain records of the statuses of each data file and each cached block using a Global Resource Directory (GRD). The GRD contents are distributed across all of the active instances.

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Q What are Oracle Clusterware Components

Voting Disk — Oracle RAC uses the voting disk to manage cluster membership by way of a health check and arbitrates cluster ownership among the instances in case of network failures. The voting disk must reside on shared disk.

Oracle Cluster Registry (OCR) — Maintains cluster configuration information as well as configuration information about any cluster database within the cluster. The OCR must reside on shared disk that is accessible by all of the nodes in your cluster

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Q How do you troubleshoot node reboot

Please check metalink ...

Note 265769.1 Troubleshooting CRS Reboots
Note.559365.1 Using Diagwait as a diagnostic to get more information for diagnosing Oracle Clusterware Node evictions.

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Q How do you backup the OCR

There is an automatic backup mechanism for OCR. The default location is : $ORA_CRS_HOME\cdata\"clustername"\

To display backups :
#ocrconfig -showbackup
To restore a backup :
#ocrconfig -restore

With Oracle RAC 10g Release 2 or later, you can also use the export command:
#ocrconfig -export -s online, and use -import option to restore the contents back.
With Oracle RAC 11g Release 1, you can do a manaual backup of the OCR with the command:
# ocrconfig -manualbackup

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Q How do you backup voting disk

#dd if=voting_disk_name of=backup_file_name

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Q How do I identify the voting disk location

#crsctl query css votedisk

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Q How do I identify the OCR file location

check /var/opt/oracle/ocr.loc or /etc/ocr.loc ( depends upon platform) or #ocrcheck

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Q Is ssh required for normal Oracle RAC operation ?

"ssh" are not required for normal Oracle RAC operation. However "ssh" should be enabled for Oracle RAC and patchset installation.

________________________________________
Q What is SCAN?

Single Client Access Name (SCAN) is s a new Oracle Real Application Clusters (RAC) 11g Release 2 feature that provides a single name for clients to access an Oracle Database running in a cluster. The benefit is clients using SCAN do not need to change if you add or remove nodes in the cluster.

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Q What is the purpose of Private Interconnect ?

Clusterware uses the private interconnect for cluster synchronization (network heartbeat) and daemon communication between the the clustered nodes. This communication is based on the TCP protocol.
RAC uses the interconnect for cache fusion (UDP) and inter-process communication (TCP). Cache Fusion is the remote memory mapping of Oracle buffers, shared between the caches of participating nodes in the cluster.

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Q Why do we have a Virtual IP (VIP) in Oracle RAC?

Without using VIPs or FAN, clients connected to a node that died will often wait for a TCP timeout period (which can be up to 10 min) before getting an error. As a result, you don't really have a good HA solution without using VIPs.
When a node fails, the VIP associated with it is automatically failed over to some other node and new node re-arps the world indicating a new MAC address for the IP. Subsequent packets sent to the VIP go to the new node, which will send error RST packets back to the clients. This results in the clients getting errors immediately

________________________________________
Q What do you do if you see GC CR BLOCK LOST in top 5 Timed Events in AWR Report?

This is most likely due to a fault in interconnect network.
Check netstat -s if you see "fragments dropped" or "packet reassemblies failed" , Work with your system administrator find the fault with network.

________________________________________
Q How many nodes are supported in a RAC Database?

10g Release 2, support 100 nodes in a cluster using Oracle Clusterware, and 100 instances in a RAC database.

________________________________________

Q Srvctl cannot start instance, I get the following error PRKP-1001 CRS-0215, however sqlplus can start it on both nodes? How do you identify the problem?

Set the environmental variable SRVM_TRACE to true.. And start the instance with srvctl. Now you will get detailed error stack.

________________________________________

Q what is the purpose of the ONS daemon?

The Oracle Notification Service (ONS) daemon is an daemon started by the CRS clusterware as part of the nodeapps. There is one ons daemon started per clustered node.
The Oracle Notification Service daemon receive a subset of published clusterware events via the local evmd and racgimon clusterware daemons and forward those events to application subscribers and to the local listeners.

This in order to facilitate:

a. the FAN or Fast Application Notification feature or allowing applications to respond to database state changes.
b. the 10gR2 Load Balancing Advisory, the feature that permit load balancing accross different rac nodes dependent of the load on the different nodes. The rdbms MMON is creating an advisory for distribution of work every 30seconds and forward it via racgimon and ONS to listeners and applications.

________________________________________
Q How do users connect to database in an Oracle RAC environment?
Users can access a RAC database using a client/server configuration or through one or more middle tiers, with or without connection pooling. Users can use oracle services feature to connect to database.

________________________________________
Q What is the use of a service in Oracle RAC environment?
Applications should use the services feature to connect to the Oracle database. Services enable us to define rules and characteristics to control how users and applications connect to database instances.

________________________________________
Q What are the characteristics controlled by Oracle services feature?
The characteristics include a unique name, workload balancing and failover options, and high availability characteristics.

________________________________________
Q What is a voting disk?
A voting disk is a file that manages information about node membership.

________________________________________
Q What are the administrative tasks involved with voting disk?
Following administrative tasks are performed with the voting disk :
1) Backing up voting disks
2) Recovering Voting disks
3) Adding voting disks
4) Deleting voting disks
5) Moving voting disks

________________________________________
Q How do we backup voting disks?
1) Oracle recommends that you back up your voting disk after the initial cluster creation and after we complete any node addition or deletion procedures.
2) First, as root user, stop Oracle Clusterware (with the crsctl stop crs command) on all nodes. Then, determine the current voting disk by issuing the following command: crsctl query votedisk css
3) Then, issue the dd or ocopy command to back up a voting disk, as appropriate.
Give the syntax of backing up voting disks:-
On Linux or UNIX systems: dd if=voting_disk_name of=backup_file_name where, voting_disk_name is the name of the active voting disk backup_file_name is the name of the file to which we want to back up the voting disk contents
On Windows systems, use the ocopy command: ocopy voting_disk_name backup_file_name

________________________________________
Q What is the Oracle Recommendation for backing up voting disk?
Oracle recommends us to use the dd command to backup the voting disk with a minimum block size of 4KB.

________________________________________
Q How do you restore a voting disk?
To restore the backup of your voting disk, issue the dd or ocopy command for Linux and UNIX systems or ocopy for Windows systems respectively.
On Linux or UNIX systems: dd if=backup_file_name of=voting_disk_name
On Windows systems, use the ocopy command: ocopy backup_file_name voting_disk_name where, backup_file_name is the name of the voting disk backup file voting_disk_name is the name of the active voting disk

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Q How can we add and remove multiple voting disks?
If we have multiple voting disks, then we can remove the voting disks and add them back into our environment using the following commands, where path is the complete path of the location where the voting disk resides: crsctl delete css votedisk path crsctl add css votedisk path

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Q How do we stop Oracle Clusterware?When do we stop it?
Before making any modification to the voting disk, as root user, stop Oracle Clusterware using the crsctl stop crs command on all nodes.

________________________________________
Q How do we add voting disk?
To add a voting disk, issue the following command as the root user, replacing the path variable with the fully qualified path name for the voting disk we want to add: crsctl add css votedisk path -force

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Q How do we move voting disks?
To move a voting disk, issue the following commands as the root user, replacing the path variable with the fully qualified path name for the voting disk we want to move: crsctl delete css votedisk path -force crsctl add css votedisk path -force

________________________________________
Q How do we remove voting disks?
To remove a voting disk, issue the following command as the root user, replacing the path variable with the fully qualified path name for the voting disk we want to remove: crsctl delete css votedisk path -force

________________________________________
Q What should we do after modifying voting disks?
After modifying the voting disk, restart Oracle Clusterware using the crsctl start crs command on all nodes, and verify the voting disk location using the following command: crsctl query css votedisk

Q When can we use -force option?
If our cluster is down, then we can include the -force option to modify the voting disk configuration, without interacting with active Oracle Clusterware daemons. However, using the -force option while any cluster node is active may corrupt our configuration.

Oracle Data Guard Interview Questions and Answers

1. How to setup Data Guard? http://www.oracle-base.com/articles/11g/data-guard-setup-11gr2.php 2. What are different types of modes in Data Guard and which is default?
Maximum performance:
This is the default protection mode. It provides the highest level of data protection that is possible without affecting the performance of a primary database. This is accomplished by allowing transactions to commit as soon as all redo data generated by those transactions has been written to the online log.

Maximum protection:
This protection mode ensures that no data loss will occur if the primary database fails. To provide this level of protection, the redo data needed to recover a transaction must be written to both the online redo log and to at least one standby database before the transaction commits. To ensure that data loss cannot occur, the primary database will shut down, rather than continue processing transactions.

Maximum availability:
This protection mode provides the highest level of data protection that is possible without compromising the availability of a primary database. Transactions do not commit until all redo data needed to recover those transactions has been written to the online redo log and to at least one standby database.

3. How many standby databases we can create (in 10g/11g)?
Till Oracle 10g, 9 standby databases are supported.
From Oracle 11g R2, we can create 30 standby databases.

4. What are the parameters we’ve to set in primary/standby for Data Guard? Parameter | Primary Role? | Standby Role? | Notes and Recommendations | ARCHIVE_LAG_TARGET = seconds | Yes | Physical only | Optional. Forces a log switch after the specified number of seconds elapses. | COMPATIBLE = release_number. | Yes | Logical and physical | Data Guard requires a minimum value of 9.2.0.1.0. Set to a minimum of 10.2.0.0 to use Oracle Database 10g new features. Specify the same value on the primary and standby databases if you expect to do a switchover. If the values differ, redo transport services may be unable to transmit redo data from the primary database to the standby databases. See Section 3.2.3 for an example.For rolling upgrades using SQL Apply, set this parameter according to the guidelines described in Section 11.4, "Prepare to Upgrade". | CONTROL_FILE_RECORD_KEEP_TIME = number_of_days | Yes | Logical and physical | Optional. Use this parameter to avoid overwriting a reusable record in the control file (that contains needed information such as an archived redo log file) for the specified number of days (from 0 to 365). See Section 5.7.4. | CONTROL_FILES = 'control_file_name' , control_file_name', '...') | Yes | Logical and physical | Required. Specify the path name and filename for one or more control files. The control files must already exist on the database. Oracle recommends using 2 control files. If another copy of the current control file is available, then an instance can be easily restarted after copying the good control file to the location of the bad control file. See Section 3.2.3 for an example. | DB_FILE_NAME_CONVERT = (location_of_primary_database_datafile' , 'location_of_standby_database_datafile_name' , '...' | No | Physical only | Required if the standby database is on the same system as the primary database or if the directory where the datafiles are located on the standby system is different from the primary system. This parameter must specify paired strings. The first string is a sequence of characters to be looked for in a primary database filename. If that sequence of characters is matched, it is replaced by the second string to construct the standby database filename. You can specify multiple pairs of filenames. See also Example 3-3. | DB_UNIQUE_NAME = unique_service_provider_name_for_this_database | Yes | Logical and physical | Recommended, but required if you specify the LOG_ARCHIVE_CONFIG parameter. Specifies a unique name for this database. This name does not change even if the primary and standby databases reverse roles. The DB_UNIQUE_NAME parameter defaults to the value of the DB_NAME parameter. See also the LOG_ARCHIVE_CONFIG parameter and Section 5.4.2. | FAL_CLIENT = Oracle_Net_service_name | Yes | Physical only | Required if the FAL_SERVER parameter is specified. Specifies the Oracle Net service name used by the FAL server (typically the primary database) to refer to the FAL client (standby database). See Section 5.8.3. | FAL_SERVER = Oracle_Net_service_name | No | Physical only | Required if the FAL_CLIENT parameter is specified. Specifies one or more Oracle Net service names for the databases from which this standby database can fetch (request) missing archived redo log files. See Section 5.8.3. | INSTANCE_NAME | Yes | Logical and physical | Optional. If this parameter is defined and the primary and standby databases reside on the same host, specify a different name for the standby database than you specify for the primary database. See Section 3.2.3 for an example. | LOG_ARCHIVE_CONFIG='DG_CONFIG=(db_unique_name, db_unique_name, ...)' | Yes | Logical and physical | Recommended. Specify the DG_CONFIG attribute to identify the DB_UNIQUE_NAME for the primary database and each standby database in the Data Guard configuration. The default value of this parameter enables the primary database to send redo data to remote destinations and enables standby databases to receive redo data. The DG_CONFIG attribute must be set to enable the dynamic addition of a standby database to a Data Guard configuration that has a Real Application Clusters primary database running in either maximum protection or maximum availability mode. See Section 5.4.2. | LOG_ARCHIVE_DEST_n = {LOCATION=path_name| SERVICE=service_name, attribute, attribute, ... } | Yes | Logical and physical | Required. Define up to ten (where n = 1, 2, 3, ... 10) destinations, each of which must specify either the LOCATION or SERVICE attribute. Specify a corresponding LOG_ARCHIVE_DEST_STATE_n parameter for every LOG_ARCHIVE_DEST_n parameter. See Section 5.2.2 and Chapter 14 for more information. | LOG_ARCHIVE_DEST_STATE_n = {ENABLE|DEFER|ALTERNATE|RESET} | Yes | Logical and physical | Required. Specify a LOG_ARCHIVE_DEST_STATE_n parameter to enable or disable redo transport services to transmit redo data to the specified (or to an alternate) destination. Define a LOG_ARCHIVE_DEST_STATE_n parameter for every LOG_ARCHIVE_DEST_n parameter. See also Section 5.2.2 and Chapter 14. | LOG_ARCHIVE_FORMAT=log%d_%t_%s_%r.arc | Yes | Logical and physical | Required if you specify the STANDBY_ARCHIVE_DEST parameter. These parameters are concatenated together to generate fully qualified archived redo log filenames on the standby database. See also Section 5.7.1. | LOG_ARCHIVE_LOCAL_FIRST =[TRUE|FALSE] | Yes | No | Optional. Specify to control when archiver processes (ARCn) transmit; either after (TRUE) the online redo log file was successfully archived to at least one local destination, or at the same time (FALSE) the online redo log file is being archived to local destinations.See also Section 5.3.1. | LOG_ARCHIVE_MAX_PROCESSES =integer | Yes | Logical and physical | Optional. Specify the number (from 1 to 30) of archiver (ARCn) processes you want Oracle software to invoke initially. The default value is 4. See Section 5.3.1.2 for more information about ARCn processing. | LOG_ARCHIVE_MIN_SUCCEED_DEST=integer | Yes | No | Optional. Define the minimum number (from 1 to 10) of destinations that must receive redo data successfully before the log writer process on the primary database can reuse the online redo log file. | LOG_ARCHIVE_TRACE=integer | Yes | Logical and physical | Optional. Set this parameter to trace the transmission of redo data to the standby site. The valid integer values (0, 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, or 4096) are described in Appendix G. | LOG_FILE_NAME_CONVERT='location_of_primary_database_redo_logs', 'location_of_standby_database_redo_logs' | No | Logical and physical | Required when the standby database is on the same system as the primary database or when the directory structure where the log files are located on the standby site is different from the primary site. This parameter converts the path names of the primary database online redo log file to path names on the standby database. See Section 3.2.3 for an example. | PARALLEL_MAX_SERVERS=integer | Yes | Logical only | Required. Specify the maximum number of parallel servers working on the logical standby database. This parameter must not be set to a value less than 5 on a logical standby database. For best results, set PARALLEL_MAX_SERVERS to a minimum of 9. | REMOTE_LOGIN_PASSWORDFILE= {EXCLUSIVE|SHARED] | Yes | Logical and physical | Required. Specify on the primary and all standby databases. | SHARED_POOL_SIZE = bytes | Yes | Logical and physical | Optional. Use to specify the system global area (SGA) to stage the information read from the online redo log files. The more SGA that is available, the more information that can be staged. | SORT_AREA_SIZE = bytes | Yes | Logical and physical | Optional. Increase the SORT_AREA_SIZE size (default size is 65536 bytes) to improve the efficiency of large sorts. See also Section 8.2. | STANDBY_ARCHIVE_DEST= filespec | No | Logical and physical | Optional. Specify the location of archived redo log files received on the standby database from the primary database. The STANDBY_ARCHIVE_DEST initialization parameter overrides the directory location specified with the LOG_ARCHIVE_DEST_n parameter. STANDBY_ARCHIVE_DEST and LOG_ARCHIVE_FORMAT are concatenated to generate fully qualified log filenames. See Section 5.7.1. | STANDBY_FILE_MANAGEMENT = {AUTO|MANUAL} | Yes | Physical only | Set the STANDBY_FILE_MANAGEMENT parameter to AUTO so that when datafiles are added to or dropped from the primary database, corresponding changes are made in the standby database without manual intervention. If the directory structures on the primary and standby databases are different, you must also set the DB_FILE_NAME_CONVERT initialization parameter to convert the filenames of one or more sets of datafiles on the primary database to filenames on the (physical) standby database. See Example 3-3 for more information and examples. | USER_DUMP_DEST = directory_path_name_of_trace_file | Yes | Logical and physical | Required if you specify the LOG_ARCHIVE_TRACE parameter. The USER_DUMP_DEST specifies the path name for a directory where the server will write debugging trace files. See Appendix G. |

5. What is the use of fal_server & fal_client, is it mandatory to set these?
The fal_server and fal_client are init.ora parameters are used for the gap resolution.

When MRP finds that an archive log is missing during media recovery, it sends the fal_client information to the server identified by fal_server and requests fal_server to resend the file again. The fal_client and fal_server init.ora (spfile) parameters are set on the standby instance.
The Oracle docs note that fal_server specifies the FAL (fetch archive log) server for a standby database. The value for fal_server is an Oracle*Net service name, which is assumed to be configured properly on the standby database system to point to the desired FAL server.
The fal_client specifies the FAL (fetch archive log) client name that is used by the FAL service, configured through the fal_server initialization parameter, to refer to the FAL client. The value of fal_client is an Oracle Net service name, which is assumed to be configured properly on the FAL server system to point to the FAL client (standby database).

6. What are differences between physical, logical, snapshot standby and ADG (or) what are different types of standby databases?
Physical standby – in mount state, MRP will apply archives
ADG – in READ ONLY state, MRP will apply archives
Logical standby – in READ ONLY state, LSP will run
Snapshot standby databases – Physical standby database can be converted to snapshot standby database, which will be in READ WRITE mode, can do any kind of testing, then we can convert back snapshot standby database to physical standby database and start MRP which will apply all pending archives.

7. How to find out backlog(gap) of standby? select round((sysdate - a.NEXT_TIME)*24*60) as "Backlog",m.SEQUENCE#-1 "Seq Applied",m.process, m.status from v$archived_log a, (select process,SEQUENCE#, status from v$managed_standby where process like '%MRP%')m where a.SEQUENCE#=(m.SEQUENCE#-1);

8. If you didn't have access to the standby database and you wanted to find out what error has occurred in a data guard configuration, what view would you check in the primary database to check the error message?
You can check the v$dataguard_status view. select message from v$dataguard_status;

9. How can u recover standby which far behind from primary (or) without archive logs how can we make standby sync?
By using RMAN incremental backup.

10. What is snapshot standby (or) How can we give a physical standby to user in READ WRITE mode and let him do updates and revert back to standby?
Till Oralce 10g, create guaranteed restore point, open in read write, let him do updates, flashback to restore point, start MRP.
From Oracle 11g, convert physical standby to snapshot standby, let him do updates, convert to physical standby, start MRP.

11. What are new features in 11g Data Guard? * Easier creation of standby database * Active Dataguard * Snapshot standby * Redo compression * Conversion from physical to logical standby * Rolling upgrade * Net timeout * Dynamically Alterable Parameters * SQL Apply Event table http://www.oracle.com/technetwork/articles/sql/11g-dataguard-083323.html 12. What are the uses of standby redo log files?
Standby Redo Logs (SRL): is similar to Online Redo Log (ORL) and only difference between two is that Standby Redo Log is used to store redo data received from another database (primary database). Standby Redo Logs are only used if you have the LGWR as transport mode to Remote Standby Database. (step to check transport mode below).
In what scenarios Standby Redo Logs are required?
Standby Redo Log is required if
1) your standby database is in maximum protection or maximum availability modes. (Physical Standby Database can run in one of three modes – Maximum Protection, Maximum Availability and Maximum Performance) or 2) If you are using Real-Time Apply on Standby Database. or 3) If you are using Cascaded Destinations.
Things good to know about SRL
i) Standby Redo Logs should be same size as of Online Redo Logs. (The RFS process will attach Standby Redo Logs only if they are of same size as of Online Redo Log) ii) Although the standby redo log is only used when the database is running in the standby role, Oracle recommends that you create a standby redo log on the primary database so that the primary database can switch over quickly to the standby role without the need for additional DBA intervention. iii) Standby redo logs can be created even after the standby has been created. In this case create the SRL’s on the primary before the creation of SRL on the standby database. (Standby Redo Log is not mandatory for Primary Database but its good practice and useful in role conversion from Primary to Standby Database) iv)It is a best practice/recommendation to maintain Standby Redo Logs (SRLs) on both the standby AND primary database when using LGWR transport mode regardless of protection mode (Maximum Protection/Performance/Availability).
13. What is RFS process on Standby Database?
RFS – Remote File System on standby database receives data from Primary Database and writes it to Disk.
14. How to identify which transport mode (Archiver or Log Writer) you are using to ship ?
SQL> show parameter log_archive_dest_ log_archive_dest_<n> SERVICE=visr12_standby [ARCH | LGWR] If neither the ARCH or LGWR attribute is specified, the default is ARCH.
More information about log_archive_dest_<n> here
15. How to check if you are using Real-Time Apply?
SQL> SELECT DEST_ID, RECOVERY_MODE FROM V$ARCHIVE_DEST_STATUS;
16. How to identify standby redo logs?
SQL> select * from v$standby_log;
17. How to see members of standby redo log file
SQL> select * from v$logfile where type=’STANDBY’;
18. How to add Standby Redo Log File Group to a Specific Group Number
SQL> alter database add standby logfile group 4 (
‘/<full_path_for_srl>/log04a.dbf’,
‘/<full_path_for_srl>/log04b.dbf’
) size 50m;

19. What is dg_config?
LOG_ARCHIVE_CONFIG='DG_CONFIG=(db_unique_name, db_unique_name, ...)' dg_config – Specifies a list of up to nine service provider names (defined with the sp_name initialization parameter) for all of the databases in the Data Guard configuration.
With dg_config, you can dynamically add a database to the Data Guard configuration while in maximum availability or maximum protection mode without shutting down databases.
Recommended. Specify the DG_CONFIG attribute to identify the DB_UNIQUE_NAME for the primary database and each standby database in the Data Guard configuration. The default value of this parameter enables the primary database to send redo data to remote destinations and enables standby databases to receive redo data. The DG_CONFIG attribute must be set to enable the dynamic addition of a standby database to a Data Guard configuration that has a Real Application Clusters primary database running in either maximum protection or maximum availability mode.

20. What is RTA (real time apply) mode MRP?
Data Guard With Real Time
Redo data is applied to the standby database as soon as it is received from the primary database. In Oracle9i, this apply has to wait till an archive log is created on the standby database For Redo Apply:
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE USING CURRENT LOGFILE
For SQL Apply:
ALTER DATABASE START LOGICAL STANDBY APPLY IMMEDIATE
When real time apply is enabled, RECOVERY_MODE column in V$ARCHIVE_DEST_STATUS displays “MANAGED REAL TIME APPLY”
Real Time Apply – Benefits * Standby databases now more closely synchronized with the primary * More up-to-date, real-time reporting * Faster switchover and failover times * Reduces planned and unplanned downtime * Better Recovery Time Objective (RTO) for DR
Note
For Real Time We must create standby log files .Redo logs can be created even after the standby has been created .
Create the SRL's :
SQL>ALTER DATABASE ADD STANDBY LOGFILE GROUP 4 (‘C:\oracle\product\10.2.0\oradata\ORCL\StandbyRedo4.log’) SIZE 100M;
SQL>ALTER DATABASE ADD STANDBY LOGFILE GROUP 5 (‘C:\oracle\product\10.2.0\oradata\ORCL\StandbyRedo5.log’) SIZE 100M;
SQL>ALTER DATABASE ADD STANDBY LOGFILE GROUP 6 (‘C:\oracle\product\10.2.0\oradata\ORCL\StandbyRedo6.log’) SIZE 100M;
Converting To Real time Real-time apply:
When real-time apply is enabled, the log apply services can apply redo data as it is received, without waiting for the current standby redo log file to be archived. In this example we are going to use LGWR on the primary for redo transport just to prove that a committed record on the primary without switching a log will show up on the standby. However real-time apply will work with both LGWR and ARCH using SRL's.
Set up log_archive_dest_2 on the primary with LGWR ASYNC or SYNC log_archive_dest_2='SERVICE=to_standby LGWR ASYNC VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=standby ' shutdown and startup the primary or if done dynamically switch a log file
You will see the following message in the alert log *LGWR: Setting 'active' archival for destination LOG_ARCHIVE_DEST_2
Enable Real Time
On the standby cancel out of the current managed recovery
SQL>ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;
Place it back in recovery with Real time apply
SQL>ALTER DATABASE RECOVER MANAGED STANDBY DATABASE USING CURRENT LOGFILE DISCONNECT;

21. What is the difference between normal MRP (managed apply) and RTA MRP (real time apply)?

Once the archived redo logs have arrived, other processes (such as an ARCH (Archiver process), an MRP (Managed Recovery Process), and/or an LSP (Logical Standby Process)) may set about applying the log contents to the standby database.
And RTA , the log apply services can apply redo data as it is received, without waiting for the current standby redo log file to be archived. In this example we are going to use LGWR on the primary for redo transport just to prove that a committed record on the primary without switching a log will show up on the standby.
22. What are various parameters in log_archive_dest and it’s use?
You can choose whether to archive redo logs to a single destination or multiplex them. If you want to archive only to a single destination, you specify that destination in the LOG_ARCHIVE_DEST initialization parameter. If you want to multiplex the archived logs, you can choose whether to archive to up to ten locations (using the LOG_ARCHIVE_DEST_n parameters) or to archive only to a primary and secondary destination (using LOG_ARCHIVE_DEST and LOG_ARCHIVE_DUPLEX_DEST). The following table summarizes the multiplexing alternatives, which are further described in the sections that follow. Method | Initialization Parameter | Host | Example | 1 | LOG_ARCHIVE_DEST_n where:n is an integer from 1 to 10 | Local or remote | LOG_ARCHIVE_DEST_1 = 'LOCATION=/disk1/arc' LOG_ARCHIVE_DEST_2 = 'SERVICE=standby1' | 2 | LOG_ARCHIVE_DEST and LOG_ARCHIVE_DUPLEX_DEST | Local only | LOG_ARCHIVE_DEST = '/disk1/arc' LOG_ARCHIVE_DUPLEX_DEST = '/disk2/arc' |

23. What is the difference between SYNC/ASYNC, LGWR/ARCH, and AFFIRM/NOAFFIRM?

SYNC and ASYNC
Specifies that network I/O is to be done synchronously (SYNC) or asynchronously (ASYNC) when archival is performed using the log writer process (LGWR).
Note:
When the primary database is in maximum protection mode or maximum availability mode, destinations archiving to standby redo log files and using the log writer process are automatically placed in SYNC mode. Category | SYNC | ASYNC | Data type | Keyword | Numeric | Valid values | Not applicable | Not applicable | Default value | Not applicable | None | Requires attributes ... | None | LGWR | Conflicts with attributes ... | ASYNC | SYNC, LOCATION, ARCH | Corresponds to ... | TRANSMIT_MODE column of the V$ARCHIVE_DEST view | TRANSMIT_MODE and ASYNC_BLOCKS columns of the V$ARCHIVE_DEST view |

Usage Notes * The SYNC and ASYNC attributes are optional: * When you specify the LGWR attribute but you do not specify either the SYNC or ASYNC attribute, the default is SYNC. * When you specify the ARCH attribute, only the SYNC attribute is valid. An error message is returned if you specify the ARCH and ASYNC attributes together. * The SYNC attribute specifies that network I/O is to be performed synchronously for the destination, which means that once the I/O is initiated, the log writer process waits for the I/O to complete before continuing. The SYNC attribute is one requirement for setting up a no-data-loss environment, because it ensures the redo records are successfully transmitted to the standby destination before continuing. * The ASYNC attribute specifies that network I/O is to be performed asynchronously for the destination.
Examples
The following example shows the SYNC attribute with the LOG_ARCHIVE_DEST_n parameter.
LOG_ARCHIVE_DEST_3='SERVICE=stby1 LGWR SYNC'
LOG_ARCHIVE_DEST_STATE_3=ENABLE

ARCH and LGWR
Specifies whether redo transport services use archiver processes (ARCn) or the log writer process (LGWR) to collect transaction redo data and transmit it to standby destinations. If neither the ARCH or LGWR attributes are specified, the default is ARCH. Category | ARCH | LGWR | Data Type | Keyword | Keyword | Valid values | Not applicable | Not applicable | Default value | Not applicable | Not applicable | Requires attributes ... | None | None | Conflicts with attributes ... | LGWR, ASYNC, NET_TIMEOUT | ARCH | Corresponds to ... | ARCHIVER, PROCESS, and SCHEDULE columns of the V$ARCHIVE_DEST view | ARCHIVER, PROCESS, and SCHEDULE columsn of the V$ARCHIVE_DEST view |

Usage Notes * These attributes are optional. If neither the ARCH or LGWR attribute is specified, the default is ARCH. * Redo transport services use ARCn processes when the ARCH attribute is specified, and the log writer process when the LGWR attribute is specified.
By default, archiving is performed by ARCn processes; you must explicitly specify the LGWR attribute for redo transport services to use the LGWR process. Although you cannot specify both LGWR and ARCn processes for the same destination, you can choose to use the log writer process for some destinations, while archiver processes transmit redo data for other destinations. * If you change a destination's current archival process (for example, from the ARCn process to the LGWR process), archival processing does not change until the next log switch occurs.
Example
The following example shows the LGWR attribute with the LOG_ARCHIVE_DEST_n parameter.
LOG_ARCHIVE_DEST_3='SERVICE=denver LGWR'
LOG_ARCHIVE_DEST_STATE_3=ENABLE

AFFIRM and NOAFFIRM
Controls whether redo transport services use synchronous or asynchronous I/O to write redo data to disk * AFFIRM—specifies that all disk I/O to archived redo log files and standby redo log files is performed synchronously and completes successfully before the log writer process continues. * NOAFFIRM—specifies that all disk I/O to archived redo log files and standby redo log files is performed asynchronously; the log writer process on the primary database does not wait until the disk I/O completes before continuing. Category | AFFIRM | NOAFFIRM | Data type | Keyword | Keyword | Valid values | Not applicable | Not applicable | Default Value | Not applicable | Not applicable | Requires attributes ... | Not applicable | Not applicable | Conflicts with attributes ... | NOAFFIRM | AFFIRM | Corresponds to ... | AFFIRM and ASYNC_BLOCKS columns of the V$ARCHIVE_DEST view | AFFIRM and ASYNC_BLOCKS columns of the V$ARCHIVE_DEST view |

Usage Notes * These attributes are optional. If neither the AFFIRM nor the NOAFFIRM attribute is specified, the default is NOAFFIRM. * The AFFIRM attribute specifies that all disk I/O to archived redo log files and standby redo log files is performed synchronously and must complete before the log writer process continues. The AFFIRM attribute: * Is one of the required attributes to ensure no data loss will occur if the primary database fails. * Can be specified with either the LOCATION or SERVICE attributes for archival operations to local or remote destinations. * Can potentially affect primary database performance, as follows: * When you specify the LGWR and AFFIRM attributes, the log writer process synchronously writes the redo data to disk, control is not returned to the user until the disk I/O completes, and online redo log files on the primary database might not be reusable until archiving is complete. * When you specify the ARCH and AFFIRM attributes, ARCn processes synchronously write the redo data to disk, the archival operation might take longer, and online redo log files on the primary database might not be reusable until archiving is complete. * When you specify the ASYNC and AFFIRM attributes, performance is not affected.
Note:
When the primary database is in the maximum protection or maximum availability mode, destinations defined with the LGWR and SYNC attributes are automatically placed in AFFIRM mode. * The NOAFFIRM attribute specifies that all disk I/O to archived redo log files and standby redo log files is performed asynchronously; the log writer process on the primary database does not wait until the disk I/O completes before continuing. * The AFFIRM and NOAFFIRM attributes apply only to archived redo log files and standby redo log files on remote standby destinations and have no effect on disk I/O for the primary database's online redo log files. * These attributes can be specified with either the LOCATION attribute for local destinations or with the SERVICE attribute for remote destinations.
Examples
The following example shows the AFFIRM attribute for a remote destination.
LOG_ARCHIVE_DEST_3='SERVICE=stby1 LGWR SYNC AFFIRM'
LOG_ARCHIVE_DEST_STATE_3=ENABLE

24. What is Data Guard broker (or) what is the use of dgmgrl?
The Oracle Data Guard broker is a distributed management framework that automates and centralizes the creation, maintenance, and monitoring of Data Guard configurations. The following list describes some of the operations the broker automates and simplifies: * Creating Data Guard configurations that incorporate a primary database, a new or existing (physical, logical, or snapshot) standby database, redo transport services, and log apply services, where any of the databases could be Oracle Real Application Clusters (RAC) databases. * Adding additional new or existing (physical, snapshot, logical, RAC or non-RAC) standby databases to an existing Data Guard configuration, for a total of one primary database, and from 1 to 9 standby databases in the same configuration. * Managing an entire Data Guard configuration, including all databases, redo transport services, and log apply services, through a client connection to any database in the configuration. * Managing the protection mode for the broker configuration. * Invoking switchover or failover with a single command to initiate and control complex role changes across all databases in the configuration. * Configuring failover to occur automatically upon loss of the primary database, increasing availability without manual intervention. * Monitoring the status of the entire configuration, capturing diagnostic information, reporting statistics such as the redo apply rate and the redo generation rate, and detecting problems quickly with centralized monitoring, testing, and performance tools.
You can perform all management operations locally or remotely through the broker's easy-to-use interfaces: the Data Guard management pages in Oracle Enterprise Manager, which is the broker's graphical user interface (GUI), and the Data Guard command-line interface called DGMGRL.

25. What is StaticConnectIdentifier property used for?
The StaticConnectIdentifier configurable instance-specific property specifies the connection identifier that the DGMGRL client will use when starting database instances. If the instance specified by the SidName property is started on a different host (read from the HOST_NAME column of the V$INSTANCE view) than the host on which it had been previously started, the broker automatically updates the default value of the StaticConnectIdentifier property to incorporate the current ADDRESS attribute of the listener that is specified for the LOCAL_LISTENER initialization parameter.

26. What is failover/switchover (or) what is the difference between failover & switchover?

Switchover – This is done when both primary and standby databases are available. It is pre-planned.
Failover – This is done when the primary database is NO longer available (ie in a Disaster). It is not pre-planned.
A switchover (or graceful switchover) is a planned role reversal between the primary and the standby databases. This is used when there is a planned outage on the primary database or primary server and you do not want to have extended downtime on the primary database. The switchover allows you to switch the roles of the databases so that the standby databases now becomes a primary databases and all your users and applications can continue operations on the “new” primary database (on the standby server). During the switchover operation there is a small outage. How long the outage lasts, depends on a number of factors including the network, the number and sizes of the redo logs. The switchover operation happens on both the primary and standby database.
A failover operation is what happens when the primary database is no longer available. The failover operation only happens on the standby database. The failover operation activates the standby database and turns this into a primary database. This process cannot be reversed so the decision to failover should be carefully made. The failover process is initiated during a real disaster or severe outage.
Automatic Failover
Automatic failover is where the software determines when the standby database should be activated to become the new primary database. There are numerous conditions that can occur (ie: network glitches/outages) in any system which theoretically could disrupt communications between the primary and standby sites. Because of the importance of this decision and the number of variances, we believe it is best not to automate this process but to leave it in the hands of a human.

27. What are the background processes involved in Data Guard?
MRP, LSP, RFS

28. Can Oracle's Data Guard be used on Standard Edition, and if so how? How can you test that the standby database is in sync?

Oracle's Data Guard technology is a layer of software and automation built on top of the standby database facility. In Oracle Standard Edition it is possible to be a standby database, and update it *manually*. Roughly, put your production database in archivelog mode. Create a hotbackup of the database and move it to the standby machine. Then create a standby controlfile on the production machine, and ship that file, along with all the archived redolog files to the standby server. Once you have all these files assembled, place them in their proper locations, recover the standby database, and you're ready to roll. From this point on, you must manually ship, and manually apply those archived redologs to stay in sync with production.

To test your standby database, make a change to a table on the production server, and commit the change. Then manually switch a logfile so those changes are archived. Manually ship the newest archived redolog file, and manually apply it on the standby database. Then open your standby database in read-only mode, and select from your changed table to verify those changes are available. Once you're done, shutdown your standby and startup again in standby mode.

29. What is the difference between Active Dataguard, and the Logical Standby implementation of 10g dataguard?
Active dataguard is mostly about the physical standby.

Use physical standby for testing without compromising protection of the production system. You can open the physical standby read/write - do some destructive things in it (drop tables, change data, whatever - run a test - perhaps with real application testing). While this is happening, redo is still streaming from production, if production fails - you are covered. Use physical standby for reporting while in managed recovery mode. Since physical standby supports all of the datatypes - and logical standby does not (11g added broader support, but not 100%) - there are times when logical standby isn’t sufficient. It also permits fast incremental backups when offloading backups to a physical standby database.
30. What is a Dataguard?

Oracle Dataguard is a disaster recovery solution from Oracle Corporation that has been utilized in the industry extensively at times of Primary site failure, failover, switchover scenarios.
31. What are the uses of Oracle Data Guard?

a) Oracle Data Guard ensures high availability, data protection, and disaster recovery for enterprise data.

b) Data Guard provides a comprehensive set of services that create, maintain, manage, and monitor one or more standby databases to enable production Oracle databases to survive disasters and data corruptions.

c) With Data Guard, administrators can optionally improve production database performance by offloading resource-intensive backup and reporting operations to standby systems.

32. What is Redo Transport Services?

It control the automated transfer of redo data from the production database to one or more archival destinations.

Redo transport services perform the following tasks:

a) Transmit redo data from the primary system to the standby systems in the configuration.
b) Manage the process of resolving any gaps in the archived redo log files due to a network failure.
c) Automatically detect missing or corrupted archived redo log files on a standby system and automatically retrieve replacement archived redo log files from the primary database or another standby database.

33. What is apply services?

Apply redo data on the standby database to maintain transactional synchronization with the primary database. Redo data can be applied either from archived redo log files, or, if real-time apply is enabled, directly from the standby redo log files as they are being filled, without requiring the redo data to be archived first at the standby database. It also allows read-only access to the data.

34. What is difference between physical and standby databases?

The main difference between physical and logical standby databases is the manner in which apply services apply the archived redo data:

a) For physical standby databases, Data Guard uses Redo Apply technology, which applies redo data on the standby database using standard recovery techniques of an Oracle database.

b) For logical standby databases, Data Guard uses SQL Apply technology, which first transforms the received redo data into SQL statements and then executes the generated SQL statements on the logical standby database.

35. What is Data Guard Broker?

Data guard Broker manage primary and standby databases using the SQL command-line interfaces or the Data Guard broker interfaces, including a command-line interface (DGMGRL) and a graphical user interface that is integrated in Oracle Enterprise Manager. It can be used to perform:

a) Create and enable Data Guard configurations, including setting up redo transport services and apply services
b) Manage an entire Data Guard configuration from any system in the configuration
c) Manage and monitor Data Guard configurations that contain Oracle RAC primary or standby databases
d) Simplify switchovers and failovers by allowing you to invoke them using either a single key click in Oracle Enterprise Manager or a single command in the DGMGRL command-line interface.
e) Enable fast-start failover to fail over automatically when the primary database becomes unavailable. When fast-start failover is enabled, the Data Guard broker determines if a failover is necessary and initiates the failover to the specified target standby database automatically, with no need for DBA intervention.

36. What are the Data guard Protection modes and summarize each?

Maximum availability :

This protection mode provides the highest level of data protection that is possible without compromising the availability of a primary database. Transactions do not commit until all redo data needed to recover those transactions has been written to the online redo log and to at least one standby database.

Maximum performance :

This is the default protection mode. It provides the highest level of data protection that is possible without affecting the performance of a primary database. This is accomplished by allowing transactions to commit as soon as all redo data generated by those transactions has been written to the online log.

Maximum protection :

This protection mode ensures that no data loss will occur if the primary database fails. To provide this level of protection, the redo data needed to recover a transaction must be written to both the online redo log and to at least one standby database before the transaction commits. To ensure that data loss cannot occur, the primary database will shut down, rather than continue processing transactions.

37. If you didn’t have access to the standby database and you wanted to find out what error has occurred in a data guard configuration, what view would you check in the primary database to check the error message?

You can check the v$dataguard_status view. Select message from v$dataguard_status;

38. In Oracle 11g, what command in RMAN can you use to create the standby database while the target database is active?
Oracle 11g has made it extremely simple to set up a standby database environment because Recovery Manager (RMAN) now supports the ability to clone the existing primary database directly to the intended standby database site over the network via the DUPLICATE DATABASE command set while the target database is active. RMAN automatically generates a conversion script in memory on the primary site and uses that script to manage the cloning operation on the standby site with virtually no DBA intervention required. You can execute this in a run block in RMAN: duplicate target database for standby dorecover from active database;

39. What additional standby database mode does Oracle 11g offer?
Oracle 11g has introduced the Oracle Snapshot Standby Database. In Snapshot Standby Database a physical standby database can easily open in read-write mode and again you can convert it back to the physical standby database. This is suitable for test and development environments and also maintains protection by continuing to receive data from the production database and archiving it for later use.

40. In Oracle 11g how can speed up backups on the standby database?
In Oracle 11g, block change tracking is now supported in the standby database.

41. With the availability of Active Data Guard, what role does SQL Apply (logical standby) continue to play?
Use SQL Apply for the following requirements: (a) when you require read-write access to a synchronized standby database but do not modify primary data, (b) when you wish to add local tables to the standby database that can also be updated, or (c) when you wish to create additional indexes to optimize read performance. The ability to handle local writes makes SQL Apply better suited to packaged reporting applications that often require write access to local tables that exist only at the target database. SQL Apply also provides rolling upgrade capability for patchsets and major database releases. This rolling upgrade functionality can also be used by physical standby databases beginning with Oracle 11g using Transient Logical Standby.

42. Why would I use Active Data Guard and not simply use SQL Apply (logical standby) that is included with Data Guard 11g?
If read-only access satisfies the requirement – Active Data Guard is a closer fit for the requirement, and therefore is much easier to implement than any other approach. Active Data Guard supports all datatypes and is very simple to implement. An Active Data Guard replica can also easily support additional uses – offloading backups from the primary database, serve as an open read-write test system during off-peak hours (Snapshot Standby), and provide an exact copy of the production database for disaster recovery – fully utilizing standby servers, storage and software while in standby role.

43. Why do I need the Oracle 11g Active Data Guard Option?
Previous capabilities did not allow Redo Apply to be active while a physical standby database was open read-only, and did not enable RMAN block change tracking on the standby database. This resulted in (a) read-only access to data that was frozen as of the time that the standby database was opened read-only, (b) failover and switchover operations that could take longer to complete due to the backlog of redo data that would need to be applied, and (c) incremental backups that could take up to 20x longer to complete – even on a database with a moderate rate of change. Previous capabilities are still included with Oracle Data Guard 11g, no additional license is required to use previous capabilities.

44. If you wanted to upgrade your current 10g physical standby data guard configuration to 11g, can you upgrade the standby to 11g first then upgrade the primary ?
Yes, in Oracle 11g, you can temporarily convert the physical standby database to a logical standby database to perform a rolling upgrade. When you issue the convert command you need to keep the identity: alter database recover logical standby keep identity;

45. If you have a low-bandwidth WAN network, what can you do to improve the Oracle 11g data guard configuration in a GAP detected situation?
Oracle 11g introduces the capability to compress redo log data as it transports over the network to the standby database. It can be enabled using the compression parameter. Compression becomes enabled only when a gap exists and the standby database needs to catch up to the primary database. alter system set log_archive_dest_1=’SERVICE=DBA11GDR COMPRESSION=ENABLE’;

46. In an Oracle 11g Logical Standby Data Guard configuration, how can you tell the dbms_scheduler to only run jobs in primary database?
Oracle 11g, logical standby now provides support for DBMS_SCHEDULER. It is capable of running jobs in both primary and logical standby database. You can use the DBMS_SCHEDULER.SET_ATTRIBUTE procedure to set the database_role. You can specify that the jobs can run only when operating in that particular database role.

47. How can you control when an archive log can be deleted in the standby database in oracle 11g ?
In Oracle 11g, you can control it by using the log_auto_delete initialization parameter. The log_auto_delete parameter must be coupled with the log_auto_del_retention_target parameter to specify the number of minutes an archivelog is maintained until it is purged. Default is 24 hours. For archivelog retention to be effective, the log_auto_delete parameter must be set to true.

48. Can Oracle Data Guard be used with Standard Edition of Oracle ?
Yes and No. The automated features of Data Guard are not available in the standard edition of Oracle. You can still however, perform log shipping manually and write scripts to manually perform the steps. If you are on unix platform, you can write shell scripts that identify the logs and then use the scp or sftp command to ship it to the standby server. Then on the standby server, identify which logs have not been applied and apply/recover them maually and remove them once applied.
49. What are the types of Oracle Data Guard?
Oracle Data Guard classified in to two types based on way of creation and method used for Redo Apply. They are as follows. 1. Physical standby (Redo Apply technology) 2. Logical standby (SQL Apply Technology)

50. What are the advantages in using Oracle Data Guard?
Following are the different benefits in using Oracle Data Guard feature in your environment. * High Availability. * Data Protection. * Off loading Backup operation to standby database. * Automatic Gap detection and Resolution in standby database. * Automatic Role Transition using Data Guard Broker.

51.What are the different services available in Oracle Data Guard?
Following are the different Services available in Oracle Data Guard of Oracle database.
1. Redo Transport Services.
2. Log Apply Services.
3. Role Transitions.

52.What are the different Protection modes available in Oracle Data Guard?
Following are the different protection modes available in Data Guard of Oracle database you can use any one based on your application requirement.
1. Maximum Protection
2. Maximum Availability
3. Maximum Performance

53.How to check what protection mode of primary database in your Oracle Data Guard?
By using following query you can check protection mode of primary database in your Oracle Data Guard setup.
SELECT PROTECTION_MODE FROM V$DATABASE;
For Example:
SQL> select protection_mode from v$database;
PROTECTION_MODE
——————————–
MAXIMUM PERFORMANCE

54.How to change protection mode in Oracle Data Guard setup?
By using following query your can change the protection mode in your primary database after setting up required value in corresponding LOG_ARCHIVE_DEST_n parameter in primary database for corresponding standby database.
ALTER DATABASE SET STANDBY DATABASE TO MAXIMUM [PROTECTION|PERFORMANCE|AVAILABILITY];
Example:
alter database set standby database to MAXIMUM PROTECTION;

55.What are the advantages of using Physical standby database in Oracle Data Guard?
Advantages of using Physical standby database in Oracle Data Guard are as follows.
§ High Availability.
§ Load balancing (Backup and Reporting).
§ Data Protection.
§ Disaster Recovery.

56.What is physical standby database in Oracle Data Guard?
Oracle Standby database are divided into physical standby database or logical standby database based on standby database creation and redo log apply method. Physical standby database are created as exact copy i.e block by block copy of primary database. In physical standby database transactions happen in primary database are synchronized in standby database by using Redo Apply method by continuously applying redo data on standby database received from primary database. Physical standby database can offload the backup activity and reporting activity from Primary database. Physical standby database can be opened for read-only transactions but redo apply won’t happen during that time. But from 11g onwards using Active Data Guard option (extra purchase) you can simultaneously open the physical standby database for read-only access and apply redo logs received from primary database.

57.What is Logical standby database in Oracle Data Guard?
Oracle Standby database are divided into physical standby database or logical standby database based on standby database creation and redo log apply method. Logical standby database can be created similar to Physical standby database and later you can alter the structure of logical standby database. Logical standby database uses SQL Apply method to synchronize logical standby database with primary database. This SQL apply technology converts the received redo logs to SQL statements and continuously apply those SQL statements on logical standby database to make standby database consistent with primary database. Main advantage of Logical standby database compare to physical standby database is you can use Logical standby database for reporting purpose during SQL apply i.e Logical standby database must be open during SQL apply. Even though Logical standby database are opened for read/write mode, tables which are in synchronize with primary database are available for read-only operations like reporting, select queries and adding index on those tables and creating materialized views on those tables. Though Logical standby database has advantage on Physical standby database it has some restriction on data-types, types of DDL, types of DML and types of tables.

58.What are the advantages of Logical standby database in Oracle Data Guard?
§ Better usage of resource
§ Data Protection
§ High Availability
§ Disaster Recovery

59.What is the usage of DB_FILE_NAME_CONVERT parameter in Oracle Data Guard setup?
DB_FILE_NAME_CONVERT parameter is used in Oracle Data Guard setup that to in standby databases. DB_FILE_NAME_CONVERT parameter are used to update the location of data files in standby database. These parameter are used when you are using different directory structure in standby database compare to primary database data files location.

60.What is the usage of LOG_FILE_NAME_CONVERT parameter in Oracle Data Guard setup?
LOG_FILE_NAME_CONVERT parameter is used in Oracle Data Guard setup that to in standby databases. LOG_FILE_NAME_CONVERT parameter are used to update the location of redo log files in standby database. These parameter are used when you are using different directory structure in standby database compare to primary database redo log file location. Step for Physical Standby
These are the steps to follow:
1. Enable forced logging
2. Create a password file
3. Configure a standby redo log
4. Enable archiving
5. Set up the primary database initialization parameters
6. Configure the listener and tnsnames to support the database on both nodes col name format a20 col thread# format 999 col sequence# format 999 col first_change# format 999999 col next_change# format 999999

SELECT thread#, sequence# AS “SEQ#”, name, first_change# AS “FIRSTSCN”, next_change# AS “NEXTSCN”,archived, deleted,completion_time AS “TIME”
FROM v$archived_log
V$ log_history

61.Tell me about parameter which is used for standby database?
Log_Archive_Dest_n
Log_Archive_Dest_State_n
Log_Archive_Config
Log_File_Name_Convert
Standby_File_Managment
DB_File_Name_Convert
DB_Unique_Name
Control_Files
Fat_Client
Fat_Server
The LOG_ARCHIVE_CONFIG parameter enables or disables the sending of redo streams to the standby sites. The DB_UNIQUE_NAME of the primary database is dg1 and the DB_UNIQUE_NAME of the standby database is dg2. The primary database is configured to ship redo log stream to the standby database. In this example, the standby database service is dg2.
Next, STANDBY_FILE_MANAGEMENT is set to AUTO so that when Oracle files are added or dropped from the primary database, these changes are made to the standby databases automatically. The STANDBY_FILE_MANAGEMENT is only applicable to the physical standby databases.
Setting the STANDBY_FILE_MANAGEMENT parameter to AUTO is is recommended when using Oracle Managed Files (OMF) on the primary database. Next, the primary database must be running in ARCHIVELOG mode.
62.What are the types of Oracle Data Guard?
Oracle Data Guard classified in to two types based on way of creation and method used for Redo Apply. They are as follows. 1. Physical standby (Redo Apply technology) 2. Logical standby (SQL Apply Technology)
63. What are the advantages in using Oracle Data Guard?
Following are the different benefits in using Oracle Data Guard feature in your environment. 1. High Availability. 2. Data Protection. 3. Off loading Backup operation to standby database. 4. Automatic Gap detection and Resolution in standby database. 5. Automatic Role Transition using Data Guard Broker.
64. What are the different services available in Oracle Data Guard?
Following are the different Services available in Oracle Data Guard of Oracle database. 1. Redo Transport Services. 2. Log Apply Services. 3. Role Transitions.
65. What are the different Protection modes available in Oracle Data Guard?
Following are the different protection modes available in Data Guard of Oracle database you can use any one based on your application requirement. 1. Maximum Protection 2. Maximum Availability 3. Maximum Performance
66. How to check what protection mode of primary database in your Oracle Data Guard?
By using following query you can check protection mode of primary database in your Oracle Data Guard setup.
SELECT PROTECTION_MODE FROM V$DATABASE;
For Example:
SQL> select protection_mode from v$database;
PROTECTION_MODE
——————————–
MAXIMUM PERFORMANCE
67. How to change protection mode in Oracle Data Guard setup?
By using following query your can change the protection mode in your primary database after setting up required value in corresponding LOG_ARCHIVE_DEST_n parameter in primary database for corresponding standby database.
ALTER DATABASE SET STANDBY DATABASE TO MAXIMUM [PROTECTION|PERFORMANCE|AVAILABILITY];
Example:
alter database set standby database to MAXIMUM PROTECTION;
68. What are the advantages of using Physical standby database in Oracle Data Guard?
Advantages of using Physical standby database in Oracle Data Guard are as follows. * High Availability. * Load balancing (Backup and Reporting). * Data Protection. * Disaster Recovery.
69. What is physical standby database in Oracle Data Guard?
Oracle Standby database are divided into physical standby database or logical standby database based on standby database creation and redo log apply method. Physical standby database are created as exact copy i.e block by block copy of primary database. In physical standby database transactions happen in primary database are synchronized in standby database by using Redo Apply method by continuously applying redo data on standby database received from primary database. Physical standby database can offload the backup activity and reporting activity from Primary database. Physical standby database can be opened for read-only transactions but redo apply won’t happen during that time. But from 11g onwards using Active Data Guard option (extra purchase) you can simultaneously open the physical standby database for read-only access and apply redo logs received from primary database.
70. What is Logical standby database in Oracle Data Guard?
Oracle Standby database are divided into physical standby database or logical standby database based on standby database creation and redo log apply method. Logical standby database can be created similar to Physical standby database and later you can alter the structure of logical standby database. Logical standby database uses SQL Apply method to synchronize logical standby database with primary database. This SQL apply technology converts the received redo logs to SQL statements and continuously apply those SQL statements on logical standby database to make standby database consistent with primary database. Main advantage of Logical standby database compare to physical standby database is you can use Logical standby database for reporting purpose during SQL apply i.e Logical standby database must be open during SQL apply. Even though Logical standby database are opened for read/write mode, tables which are in synchronize with primary database are available for read-only operations like reporting, select queries and adding index on those tables and creating materialized views on those tables. Though Logical standby database has advantage on Physical standby database it has some restriction on data-types, types of DDL, types of DML and types of tables.
71. What are the advantages of Logical standby database in Oracle Data Guard? * Better usage of resource * Data Protection * High Availability * Disaster Recovery
72. What is the usage of DB_FILE_NAME_CONVERT parameter in Oracle Data Guard setup?
DB_FILE_NAME_CONVERT parameter is used in Oracle Data Guard setup that to in standby databases. DB_FILE_NAME_CONVERT parameter are used to update the location of data files in standby database. These parameter are used when you are using different directory structure in standby database compare to primary database data files location.
73. What is the usage of LOG_FILE_NAME_CONVERT parameter in Oracle Data Guard setup?
LOG_FILE_NAME_CONVERT parameter is used in Oracle Data Guard setup that to in standby databases. LOG_FILE_NAME_CONVERT parameter are used to update the location of redo log files in standby database. These parameter are used when you are using different directory structure in standby database compare to primary database redo log file location. Step for Physical Standby
These are the steps to follow: 1. Enable forced logging 2. Create a password file 3. Configure a standby redo log 4. Enable archiving 5. Set up the primary database initialization parameters 6. Configure the listener and tnsnames to support the database on both nodes col name format a20 col thread# format 999 col sequence# format 999 col first_change# format 999999 col next_change# format 999999

SELECT thread#, sequence# AS “SEQ#”, name, first_change# AS “FIRSTSCN”, next_change# AS “NEXTSCN”,archived, deleted,completion_time AS “TIME”
FROM v$archived_log
V$ log_history

74. Tell me about parameter which is used for standby database?
Log_Archive_Dest_n
Log_Archive_Dest_State_n
Log_Archive_Config
Log_File_Name_Convert
Standby_File_Managment
DB_File_Name_Convert
DB_Unique_Name
Control_Files
Fat_Client
Fat_Server
The LOG_ARCHIVE_CONFIG parameter enables or disables the sending of redo streams to the standby sites. The DB_UNIQUE_NAME of the primary database is dg1 and the DB_UNIQUE_NAME of the standby database is dg2. The primary database is configured to ship redo log stream to the standby database. In this example, the standby database service is dg2.
Next, STANDBY_FILE_MANAGEMENT is set to AUTO so that when Oracle files are added or dropped from the primary database, these changes are made to the standby databases automatically. The STANDBY_FILE_MANAGEMENT is only applicable to the physical standby databases.
-------------------------------------------------
Setting the STANDBY_FILE_MANAGEMENT parameter to AUTO is is recommended when using Oracle Managed Files (OMF) on the primary database. Next, the primary database must be running in ARCHIVELOG mode.
-------------------------------------------------

-------------------------------------------------

-------------------------------------------------

What is Dataguard?

Data Guard provides a comprehensive set of services that create, maintain, manage, and monitor one or more standby databases to enable production Oracle databases to survive disasters and data corruptions. Data Guard maintains these standby databases as copies of the production database. Data Guard can be used with traditional backup, restoration, and cluster techniques to provide a high level of data protection and data availability.

What is DG Broker?
DG Broker “it is the management and monitoring tool”.
Oracle dataguard broker is a distributed management framework that automates and centralizes the creation , maintenance and monitoring of DG configuration.
All management operations can be performed either through OEM, which uses the broker (or) broker specified command-line tool interface “DGMGRL”.

What is the difference between Dataguard and Standby?

Dataguard :
Dataguard is mechanism/tool to maintain standby database.
The dataguard is set up between primary and standby instance .
Data Guard is only available on Enterprise Edition.

Standby Database :
Physical standby database provides a physically identical copy of the primary database, with on disk database structures that are identical to the primary database on a block-for-block basis.
Standby capability is available on Standard Edition.

REFERENCE: http://neeraj-dba.blogspot.in/2011/06/difference-between-dataguard-and.html What are the differences between Physical/Logical standby databases? How would you decide which one is best suited for your environment?
Physical standby DB:
As the name, it is physically (datafiles, schema, other physical identity) same copy of the primary database.
It synchronized with the primary database with Apply Redo to the standby DB.
Logical Standby DB:
As the name logical information is the same as the production database, it may be physical structure can be different.
It synchronized with primary database though SQL Apply, Redo received from the primary database into SQL statements and then executing these SQL statements on the standby DB.
We can open “physical stand by DB to “read only” and make it available to the applications users (Only select is allowed during this period). we can not apply redo logs received from primary database at this time.
We do not see such issues with logical standby database. We can open the database in normal mode and make it available to the users. At the same time, we can apply archived logs received from primary database.

For OLTP large transaction database it is better to choose logical standby database.

Explain Active Dataguard?

11g Active Data Guard
Oracle Active Data Guard enables read-only access to a physical standby database for queries, sorting, reporting, web-based access, etc., while continuously applying changes received from the production database.
Oracle Active Data Guard also enables the use of fast incremental backups when offloading backups to a standby database, and can provide additional benefits of high availability and disaster protection against planned or unplanned outages at the production site.

What is a Snapshot Standby Database?
11g Snapshot Standby Database
Oracle 11g introduces the Snapshot Standby database which essentially is an updateable standby database which has been created from a physical standby database.
We can convert a physical standby database to a snapshot standby database, do some kind of testing on a database which is a read write copy of the current primary or production database and then finally revert it to it’s earlier state as a physical standby database.
While the snapshot standby database is open in read-write mode, redo is being received from the primary database, but is not applied.
After converting it back to a physical standby database, it is resynchronized with the primary by applying the accumalated redo data which was earlier shipped from the primary database but not applied.
Using a snapshot standby, we are able to do real time application testing using near real time production data. Very often we are required to do production clones for the purpose of testing. But using snapshot standby databases we can meet the same requirement sparing the effort,time,resources and disk space.

REFERENCE: http://gavinsoorma.com/2009/07/11g-snapshot-standby-database/ Snapshot Standby Database (UPDATEABLE SNAPSHOT FOR TESTING)
A snapshot standby database is a fully updatable standby database that is created by converting a physical standby database into a snapshot standby database.

Like a physical or logical standby database, a snapshot standby database receives and archives redo data from a primary database. Unlike a physical or logical standby database, a snapshot standby database does not apply the redo data that it receives. The redo data received by a snapshot standby database is not applied until the snapshot standby is converted back into a physical standby database, after first discarding any local updates made to the snapshot standby database.

REFERENCE: http://docs.oracle.com/cd/B28359_01/server.111/b28294/title.htm What is the Default mode will the Standby will be, either SYNC or ASYNC?
ASYNC

Dataguard Architechture?
Data Guard Configurations:
A Data Guard configuration consists of one production database and one or more standby databases. The databases in a Data Guard configuration are connected by Oracle Net and may be dispersed geographically. There are no restrictions on where the databases are located, provided they can communicate with each other.

Dataguard Architecture
The Oracle 9i Data Guard architecture incorporates the following items:

• Primary Database - A production database that is used to create standby databases. The archive logs from the primary database are transfered and applied to standby databases. Each standby can only be associated with a single primary database, but a single primary database can be associated with multiple standby databases.
• Standby Database - A replica of the primary database.
• Log Transport Services - Control the automatic transfer of archive redo log files from the primary database to one or more standby destinations.
• Network Configuration - The primary database is connected to one or more standby databases using Oracle Net.
• Log Apply Services - Apply the archived redo logs to the standby database. The Managed Recovery Process (MRP) actually does the work of maintaining and applying the archived redo logs.
• Role Management Services - Control the changing of database roles from primary to standby. The services include switchover, switchback and failover.
• Data Guard Broker - Controls the creation and monitoring of Data Guard. It comes with a GUI and command line interface.

Primary Database:
A Data Guard configuration contains one production database, also referred to as the primary database, that functions in the primary role. This is the database that is accessed by most of your applications.

Standby Database:
A standby database is a transactionally consistent copy of the primary database. Using a backup copy of the primary database, you can create up to nine standby databases and incorporate them in a Data Guard configuration. Once created, Data Guard automatically maintains each standby database by transmitting redo data from the primary database and then applying the redo to the standby database.
The types of standby databases are as follows:

Physical standby database:
Provides a physically identical copy of the primary database, with on disk database structures that are identical to the primary database on a block-for-block basis. The database schema, including indexes, are the same. A physical standby database is kept synchronized with the primary database, through Redo Apply, which recovers the redo data received from the primary database and applies the redo to the physical standby database.

Logical standby database:
Contains the same logical information as the production database, although the physical organization and structure of the data can be different. The logical standby database is kept synchronized with the primary database through SQL Apply, which transforms the data in the redo received from the primary database into SQL statements and then executes the SQL statements on the standby database.

What are the services required on the primary and standby database ?
The services required on the primary database are:
• Log Writer Process (LGWR) - Collects redo information and updates the online redo logs. It can also create local archived redo logs and transmit online redo to standby databases.
• Archiver Process (ARCn) - One or more archiver processes make copies of online redo logs either locally or remotely for standby databases.
• Fetch Archive Log (FAL) Server - Services requests for archive redo logs from FAL clients running on multiple standby databases. Multiple FAL servers can be run on a primary database, one for each FAL request. .
The services required on the standby database are:
• Fetch Archive Log (FAL) Client - Pulls archived redo log files from the primary site. Initiates transfer of archived redo logs when it detects a gap sequence.
• Remote File Server (RFS) - Receives archived and/or standby redo logs from the primary database.
• Archiver (ARCn) Processes - Archives the standby redo logs applied by the managed recovery process (MRP).
• Managed Recovery Process (MRP) - Applies archive redo log information to the standby database.

What is RTS (Redo Transport Services) in Dataguard?
It controls the automated transfer of redo data from the production database to one or more archival destinations. The redo transport services perform the following tasks:
a) Transmit redo data from the primary system to the standby systems in the configuration.
b) Manage the process of resolving any gaps in the archived redo log files due to a network failure.
c) Automatically detect missing or corrupted archived redo log files on a standby system and automatically retrieve replacement archived redo log files from the primary database or another standby database.

What are the Protection Modes in Dataguard?

Data Guard Protection Modes
This section describes the Data Guard protection modes.
In these descriptions, a synchronized standby database is meant to be one that meets the minimum requirements of the configured data protection mode and that does not have a redo gap. Redo gaps are discussed in Section 6.3.3.

Maximum Availability
This protectionmode provides the highest level of data protection that is possible without compromising the availability of a primary database. Transactions do not commit until all redo data needed to recover those transactions has been written to the online redo log and to at least one synchronized standby database. If the primary database cannot write its redo stream to at least one synchronized standby database, it operates as if it were in maximum performance mode to preserve primary database availability until it is again able to write its redo stream to a synchronized standby database.
This mode ensures that no data loss will occur if the primary database fails, but only if a second fault does not prevent a complete set of redo data from being sent from the primary database to at least one standby database.

Maximum Performance
This protectionmode provides the highest level of data protection that is possible without affecting the performance of a primary database. This is accomplished by allowing transactions to commit as soon as all redo data generated by those transactions has been written to the online log. Redo data is also written to one or more standby databases, but this is done asynchronously with respect to transaction commitment, so primary database performance is unaffected by delays in writing redo data to the standby database(s).
This protection mode offers slightly less data protection than maximum availability mode and has minimal impact on primary database performance.
This is the default protection mode.

Maximum Protection
This protection mode ensures that zero data loss occurs if a primary database fails. To provide this level of protection, the redo data needed to recover a transaction must be written to both the online redo log and to at least one synchronized standby database before the transaction commits. To ensure that data loss cannot occur, the primary database will shut down, rather than continue processing transactions, if it cannot write its redo stream to at least one synchronized standby database.
Because this data protection mode prioritizes data protection over primary database availability, Oracle recommends that a minimum of two standby databases be used to protect a primary database that runs in maximum protection mode to prevent a single standby database failure from causing the primary database to shut down.

How to delay the application of logs to a physical standby?

A standby database automatically applies redo logs when they arrive from the primary database. But in some cases, we want to create a time lag between the archiving of a redo log at the primary site, and the application of the log at the standby site.

Modify the LOG_ARCHIVE_DEST_n initialization parameter on the primary database to set a delay for the standby database.

Example: For 60min Delay:
ALTER SYSTEM SET LOG_ARCHIVE_DEST_2='SERVICE=stdby_srvc DELAY=60';
The DELAY attribute is expressed in minutes.
The archived redo logs are still automatically copied from the primary site to the standby site, but the logs are not immediately applied to the standby database. The logs are applied when the specified time interval expires.

Steps to create Physical Standby database?

1.Take a full hot backup of Primary database
2.Create standby control file
3.Transfer full backup, init.ora, standby control file to standby node.
4.Modify init.ora file on standby node.
5.Restore database
6.Recover Standby database
(Alternatively, RMAN DUPLICATE DATABASE FOR STANDBY DO RECOVERY can be also used)
7.Setup FAL_CLIENT and FAL_SERVER parameters on both sides
8.Put Standby database in Managed Recover mode

What are the DATAGUARD PARAMETERS in Oracle?
Set Primary Database Initialization Parameters
----------------------------------------------
On the primary database, you define initialization parameters that control redo transport services while the database is in the primary role. There are additional parameters you need to add that control the receipt of the redo data and log apply services when the primary database is transitioned to the standby role.

DB_NAME=chicago
DB_UNIQUE_NAME=chicago
LOG_ARCHIVE_CONFIG='DG_CONFIG=(chicago,boston)'
CONTROL_FILES='/arch1/chicago/control1.ctl', '/arch2/chicago/control2.ctl'
LOG_ARCHIVE_DEST_1=
'LOCATION=/arch1/chicago/ VALID_FOR=(ALL_LOGFILES,ALL_ROLES) DB_UNIQUE_NAME=chicago'
LOG_ARCHIVE_DEST_2=
'SERVICE=boston LGWR ASYNC VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=boston'
LOG_ARCHIVE_DEST_STATE_1=ENABLE
LOG_ARCHIVE_DEST_STATE_2=ENABLE
REMOTE_LOGIN_PASSWORDFILE=EXCLUSIVE
LOG_ARCHIVE_FORMAT=%t_%s_%r.arc
LOG_ARCHIVE_MAX_PROCESSES=30

Primary Database: Standby Role Initialization Parameters
FAL_SERVER=boston
FAL_CLIENT=chicago
DB_FILE_NAME_CONVERT='boston','chicago'
LOG_FILE_NAME_CONVERT= '/arch1/boston/','/arch1/chicago/','/arch2/boston/','/arch2/chicago/'
STANDBY_FILE_MANAGEMENT=AUTO

Prepare an Initialization Parameter File for the Standby Database
-----------------------------------------------------------------
Create a text initialization parameter file (PFILE) from the server parameter file (SPFILE) used by the primary database; a text initialization parameter file can be copied to the standby location and modified. For example:
CREATE PFILE='/tmp/initboston.ora' FROM SPFILE;

Modifying Initialization Parameters for a Physical Standby Database.

DB_NAME=chicago
DB_UNIQUE_NAME=boston
LOG_ARCHIVE_CONFIG='DG_CONFIG=(chicago,boston)'
CONTROL_FILES='/arch1/boston/control1.ctl', '/arch2/boston/control2.ctl'
DB_FILE_NAME_CONVERT='chicago','boston'
LOG_FILE_NAME_CONVERT= '/arch1/chicago/','/arch1/boston/','/arch2/chicago/','/arch2/boston/'
LOG_ARCHIVE_FORMAT=log%t_%s_%r.arc
LOG_ARCHIVE_DEST_1= 'LOCATION=/arch1/boston/
VALID_FOR=(ALL_LOGFILES,ALL_ROLES)
DB_UNIQUE_NAME=boston'
LOG_ARCHIVE_DEST_2= 'SERVICE=chicago LGWR ASYNC VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=chicago'
LOG_ARCHIVE_DEST_STATE_1=ENABLE
LOG_ARCHIVE_DEST_STATE_2=ENABLE
REMOTE_LOGIN_PASSWORDFILE=EXCLUSIVE
STANDBY_FILE_MANAGEMENT=AUTO
FAL_SERVER=chicago
FAL_CLIENT=boston

http://sarith.wordpress.com/tag/oracle-10g-data-guard/

Primary DB Dataguard Parameter?

Parameters responsible for Failover in Dataguard?

Difference between FAL_SERVER (Fetch Archive Log) Vs. FAL_Client

What is RFS?

If DR has different file location, which parameter need to be chamged?

Can we have Standby Database in STANDARD EDITION?

Can we have Primary Database in SOLARIS OS and Standby in LINUX OS?

What are DR creation Prerequisites?
Dataguard creation steps?

Why password file in dataguard?

What is Dataguard?
Data Guard provides a comprehensive set of services that create, maintain, manage, and monitor one or more standby databases to enable production Oracle databases to survive disasters and data corruptions. Data Guard maintains these standby databases as copies of the production database. Data Guard can be used with traditional backup, restoration, and cluster techniques to provide a high level of data protection and data availability.
What is DG Broker?
DG Broker “it is the management and monitoring tool”.
Oracle dataguard broker is a distributed management framework that automates and centralizes the creation , maintenance and monitoring of DG configuration.
All management operations can be performed either through OEM, which uses the broker (or) broker specified command-line tool interface “DGMGRL”.
What is the difference between Dataguard and Standby?
Dataguard :
Dataguard is mechanism/tool to maintain standby database.
The dataguard is set up between primary and standby instance .
Data Guard is only available on Enterprise Edition.
Standby Database :
Physical standby database provides a physically identical copy of the primary database, with on disk database structures that are identical to the primary database on a block-for-block basis.
Standby capability is available on Standard Edition.
REFERENCE:
http://neeraj-dba.blogspot.in/2011/06/difference-between-dataguard-and.html
What are the differences between Physical/Logical standby databases? How would you decide which one is best suited for your environment?
Physical standby DB:
As the name, it is physically (datafiles, schema, other physical identity) same copy of the primary database.
It synchronized with the primary database with Apply Redo to the standby DB.
Logical Standby DB:
As the name logical information is the same as the production database, it may be physical structure can be different.
It synchronized with primary database though SQL Apply, Redo received from the primary database into SQL statements and then executing these SQL statements on the standby DB.
We can open “physical stand by DB to “read only” and make it available to the applications users (Only select is allowed during this period). we can not apply redo logs received from primary database at this time.
We do not see such issues with logical standby database. We can open the database in normal mode and make it available to the users. At the same time, we can apply archived logs received from primary database.
For OLTP large transaction database it is better to choose logical standby database.
Explain Active Dataguard?
11g Active Data Guard
Oracle Active Data Guard enables read-only access to a physical standby database for queries, sorting, reporting, web-based access, etc., while continuously applying changes received from the production database.
Oracle Active Data Guard also enables the use of fast incremental backups when offloading backups to a standby database, and can provide additional benefits of high availability and disaster protection against planned or unplanned outages at the production site.
What is a Snapshot Standby Database?
11g Snapshot Standby Database
Oracle 11g introduces the Snapshot Standby database which essentially is an updateable standby database which has been created from a physical standby database.
We can convert a physical standby database to a snapshot standby database, do some kind of testing on a database which is a read write copy of the current primary or production database and then finally revert it to it’s earlier state as a physical standby database.
While the snapshot standby database is open in read-write mode, redo is being received from the primary database, but is not applied.
After converting it back to a physical standby database, it is resynchronized with the primary by applying the accumalated redo data which was earlier shipped from the primary database but not applied.
Using a snapshot standby, we are able to do real time application testing using near real time production data. Very often we are required to do production clones for the purpose of testing. But using snapshot standby databases we can meet the same requirement sparing the effort,time,resources and disk space.
REFERENCE:
http://gavinsoorma.com/2009/07/11g-snapshot-standby-database/
Snapshot Standby Database (UPDATEABLE SNAPSHOT FOR TESTING)
A snapshot standby database is a fully updatable standby database that is created by converting a physical standby database into a snapshot standby database.
Like a physical or logical standby database, a snapshot standby database receives and archives redo data from a primary database. Unlike a physical or logical standby database, a snapshot standby database does not apply the redo data that it receives. The redo data received by a snapshot standby database is not applied until the snapshot standby is converted back into a physical standby database, after first discarding any local updates made to the snapshot standby database.
REFERENCE:
http://docs.oracle.com/cd/B28359_01/server.111/b28294/title.htm
What is the Default mode will the Standby will be, either SYNC or ASYNC?
ASYNC
Dataguard Architechture?
Data Guard Configurations:
A Data Guard configuration consists of one production database and one or more standby databases. The databases in a Data Guard configuration are connected by Oracle Net and may be dispersed geographically. There are no restrictions on where the databases are located, provided they can communicate with each other.
Dataguard Architecture
The Oracle 9i Data Guard architecture incorporates the following items:
• Primary Database – A production database that is used to create standby databases. The archive logs from the primary database are transfered and applied to standby databases. Each standby can only be associated with a single primary database, but a single primary database can be associated with multiple standby databases.
• Standby Database – A replica of the primary database.
• Log Transport Services – Control the automatic transfer of archive redo log files from the primary database to one or more standby destinations.
• Network Configuration – The primary database is connected to one or more standby databases using Oracle Net.
• Log Apply Services – Apply the archived redo logs to the standby database. The Managed Recovery Process (MRP) actually does the work of maintaining and applying the archived redo logs.
• Role Management Services – Control the changing of database roles from primary to standby. The services include switchover, switchback and failover.
• Data Guard Broker – Controls the creation and monitoring of Data Guard. It comes with a GUI and command line interface.
Primary Database:
A Data Guard configuration contains one production database, also referred to as the primary database, that functions in the primary role. This is the database that is accessed by most of your applications.
Standby Database:
A standby database is a transactionally consistent copy of the primary database. Using a backup copy of the primary database, you can create up to nine standby databases and incorporate them in a Data Guard configuration. Once created, Data Guard automatically maintains each standby database by transmitting redo data from the primary database and then applying the redo to the standby database.
The types of standby databases are as follows:
Physical standby database:
Provides a physically identical copy of the primary database, with on disk database structures that are identical to the primary database on a block-for-block basis. The database schema, including indexes, are the same. A physical standby database is kept synchronized with the primary database, through Redo Apply, which recovers the redo data received from the primary database and applies the redo to the physical standby database.
Logical standby database:
Contains the same logical information as the production database, although the physical organization and structure of the data can be different. The logical standby database is kept synchronized with the primary database through SQL Apply, which transforms the data in the redo received from the primary database into SQL statements and then executes the SQL statements on the standby database.
What are the services required on the primary and standby database ?
The services required on the primary database are:
• Log Writer Process (LGWR) – Collects redo information and updates the online redo logs. It can also create local archived redo logs and transmit online redo to standby databases.
• Archiver Process (ARCn) – One or more archiver processes make copies of online redo logs either locally or remotely for standby databases.
• Fetch Archive Log (FAL) Server – Services requests for archive redo logs from FAL clients running on multiple standby databases. Multiple FAL servers can be run on a primary database, one for each FAL request. .
The services required on the standby database are:
• Fetch Archive Log (FAL) Client – Pulls archived redo log files from the primary site. Initiates transfer of archived redo logs when it detects a gap sequence.
• Remote File Server (RFS) – Receives archived and/or standby redo logs from the primary database.
• Archiver (ARCn) Processes – Archives the standby redo logs applied by the managed recovery process (MRP).
• Managed Recovery Process (MRP) – Applies archive redo log information to the standby database.
What is RTS (Redo Transport Services) in Dataguard?
It controls the automated transfer of redo data from the production database to one or more archival destinations. The redo transport services perform the following tasks:
a) Transmit redo data from the primary system to the standby systems in the configuration.
b) Manage the process of resolving any gaps in the archived redo log files due to a network failure.
c) Automatically detect missing or corrupted archived redo log files on a standby system and automatically retrieve replacement archived redo log files from the primary database or another standby database.
What are the Protection Modes in Dataguard?
Data Guard Protection Modes
This section describes the Data Guard protection modes.
In these descriptions, a synchronized standby database is meant to be one that meets the minimum requirements of the configured data protection mode and that does not have a redo gap. Redo gaps are discussed in Section 6.3.3.
Maximum Availability
This protectionmode provides the highest level of data protection that is possible without compromising the availability of a primary database. Transactions do not commit until all redo data needed to recover those transactions has been written to the online redo log and to at least one synchronized standby database. If the primary database cannot write its redo stream to at least one synchronized standby database, it operates as if it were in maximum performance mode to preserve primary database availability until it is again able to write its redo stream to a synchronized standby database.
This mode ensures that no data loss will occur if the primary database fails, but only if a second fault does not prevent a complete set of redo data from being sent from the primary database to at least one standby database.
Maximum Performance
This protectionmode provides the highest level of data protection that is possible without affecting the performance of a primary database. This is accomplished by allowing transactions to commit as soon as all redo data generated by those transactions has been written to the online log. Redo data is also written to one or more standby databases, but this is done asynchronously with respect to transaction commitment, so primary database performance is unaffected by delays in writing redo data to the standby database(s).
This protection mode offers slightly less data protection than maximum availability mode and has minimal impact on primary database performance.
This is the default protection mode.
Maximum Protection
This protection mode ensures that zero data loss occurs if a primary database fails. To provide this level of protection, the redo data needed to recover a transaction must be written to both the online redo log and to at least one synchronized standby database before the transaction commits. To ensure that data loss cannot occur, the primary database will shut down, rather than continue processing transactions, if it cannot write its redo stream to at least one synchronized standby database.
Because this data protection mode prioritizes data protection over primary database availability, Oracle recommends that a minimum of two standby databases be used to protect a primary database that runs in maximum protection mode to prevent a single standby database failure from causing the primary database to shut down.
How to delay the application of logs to a physical standby?
A standby database automatically applies redo logs when they arrive from the primary database. But in some cases, we want to create a time lag between the archiving of a redo log at the primary site, and the application of the log at the standby site.
Modify the LOG_ARCHIVE_DEST_n initialization parameter on the primary database to set a delay for the standby database.
Example: For 60min Delay:
ALTER SYSTEM SET LOG_ARCHIVE_DEST_2=’SERVICE=stdby_srvc DELAY=60′;
The DELAY attribute is expressed in minutes.
The archived redo logs are still automatically copied from the primary site to the standby site, but the logs are not immediately applied to the standby database. The logs are applied when the specified time interval expires.
Steps to create Physical Standby database?
1.Take a full hot backup of Primary database
2.Create standby control file
3.Transfer full backup, init.ora, standby control file to standby node.
4.Modify init.ora file on standby node.
5.Restore database
6.Recover Standby database
(Alternatively, RMAN DUPLICATE DATABASE FOR STANDBY DO RECOVERY can be also used)
7.Setup FAL_CLIENT and FAL_SERVER parameters on both sides
8.Put Standby database in Managed Recover mode
What are the DATAGUARD PARAMETERS in Oracle?
Set Primary Database Initialization Parameters
———————————————-
On the primary database, you define initialization parameters that control redo transport services while the database is in the primary role. There are additional parameters you need to add that control the receipt of the redo data and log apply services when the primary database is transitioned to the standby role.
DB_NAME=chicago
DB_UNIQUE_NAME=chicago
LOG_ARCHIVE_CONFIG=’DG_CONFIG=(chicago,boston)’
CONTROL_FILES=’/arch1/chicago/control1.ctl’, ‘/arch2/chicago/control2.ctl’
LOG_ARCHIVE_DEST_1=
‘LOCATION=/arch1/chicago/
VALID_FOR=(ALL_LOGFILES,ALL_ROLES)
DB_UNIQUE_NAME=chicago’
LOG_ARCHIVE_DEST_2=
‘SERVICE=boston LGWR ASYNC
VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE)
DB_UNIQUE_NAME=boston’
LOG_ARCHIVE_DEST_STATE_1=ENABLE
LOG_ARCHIVE_DEST_STATE_2=ENABLE
REMOTE_LOGIN_PASSWORDFILE=EXCLUSIVE
LOG_ARCHIVE_FORMAT=%t_%s_%r.arc
LOG_ARCHIVE_MAX_PROCESSES=30
Primary Database: Standby Role Initialization Parameters
FAL_SERVER=boston
FAL_CLIENT=chicago
DB_FILE_NAME_CONVERT=’boston’,'chicago’
LOG_FILE_NAME_CONVERT= ‘/arch1/boston/’,'/arch1/chicago/’,'/arch2/boston/’,'/arch2/chicago/’
STANDBY_FILE_MANAGEMENT=AUTO
Prepare an Initialization Parameter File for the Standby Database
—————————————————————–
Create a text initialization parameter file (PFILE) from the server parameter file (SPFILE) used by the primary database; a text initialization parameter file can be copied to the standby location and modified. For example:
CREATE PFILE=’/tmp/initboston.ora’ FROM SPFILE;
Modifying Initialization Parameters for a Physical Standby Database.
DB_NAME=chicago
DB_UNIQUE_NAME=boston
LOG_ARCHIVE_CONFIG=’DG_CONFIG=(chicago,boston)’
CONTROL_FILES=’/arch1/boston/control1.ctl’, ‘/arch2/boston/control2.ctl’
DB_FILE_NAME_CONVERT=’chicago’,'boston’
LOG_FILE_NAME_CONVERT= ‘/arch1/chicago/’,'/arch1/boston/’,'/arch2/chicago/’,'/arch2/boston/’
LOG_ARCHIVE_FORMAT=log%t_%s_%r.arc
LOG_ARCHIVE_DEST_1= ‘LOCATION=/arch1/boston/
VALID_FOR=(ALL_LOGFILES,ALL_ROLES)
DB_UNIQUE_NAME=boston’
LOG_ARCHIVE_DEST_2= ‘SERVICE=chicago LGWR ASYNC VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=chicago’
LOG_ARCHIVE_DEST_STATE_1=ENABLE
LOG_ARCHIVE_DEST_STATE_2=ENABLE
REMOTE_LOGIN_PASSWORDFILE=EXCLUSIVE
STANDBY_FILE_MANAGEMENT=AUTO
FAL_SERVER=chicago
FAL_CLIENT=boston

-------------------------------------------------

Oracle ASM Interview Questions and Answers

What is ASM in Oracle?
Oracle ASM is Oracle’s volume manager specially designed for Oracle database data. It is available since Oracle database version 10g and many improvements have been made in versions 11g release 1 and 2.

ASM offers support for Oracle RAC clusters without the requirement to install 3rd party software, such as cluster aware volume managers or filesystems.

ASM is shipped as part of the database server software (Enterprise and Standard editions) and does not cost extra money to run.

ASM simplifies administration of Oracle related files by allowing the administrator to reference disk groups rather than individual disks and files, which are managed by ASM.

The ASM functionality is an extention of the Oracle Managed Files (OMF) functionality that also includes striping and mirroring to provide balanced and secure storage. The new ASM functionality can be used in combination with existing raw and cooked file systems, along with OMF and manually managed files.

Advantages of ASM in Oracle?
Provides automatic load balancing over all the available disks, thus reducing hot spots in the file system

Prevents fragmentation of disks, so you don't need to manually relocate data to tune I/O performance

Adding disks is straight forward - ASM automatically performs online disk reorganization when you add or remove storage

Uses redundancy features available in intelligent storage arrays

The storage system can store all types of database files

Using disk group makes configuration easier, as files are placed into disk groups

ASM provides stripping and mirroring (fine and coarse gain - see below)

ASM and non-ASM oracle files can coexist

Striping—ASM spreads data evenly across all disks in a disk group to optimize performance and utilization. This even distribution of database files eliminates the need for regular monitoring and I/O performance tuning.

For example, if there are six disks in a disk group, pieces of each ASM file are written to all six disks. These pieces come in 1 MB chunks known as extents. When a database file is created, it is striped (divided into extents and distributed) across the six disks, and allocated disk space on all six disks grows evenly. When reading the file, file extents are read from all six disks in parallel, greatly increasing performance.

Mirroring—ASM can increase availability by optionally mirroring any file. ASM mirrors at the file level, unlike operating system mirroring, which mirrors at the disk level. Mirroring means keeping redundant copies, or mirrored copies, of each extent of the file, to help avoid data loss caused by disk failures. The mirrored copy of each file extent is always kept on a different disk from the original copy. If a disk fails, ASM can continue to access affected files by accessing mirrored copies on the surviving disks in the disk group.

ASM supports 2-way mirroring, where each file extent gets one mirrored copy, and 3-way mirroring, where each file extent gets two mirrored copies.

Online storage reconfiguration and dynamic rebalancing—ASM permits you to add or remove disks from your disk storage system while the database is operating. When you add a disk, ASM automatically redistributes the data so that it is evenly spread across all disks in the disk group, including the new disk. This redistribution is known as rebalancing. It is done in the background and with minimal impact to database performance. When you request to remove a disk, ASM first rebalances by evenly relocating all file extents from the disk being removed to the other disks in the disk group.

Managed file creation and deletion—ASM further reduces administration tasks by enabling files stored in ASM disk groups to be Oracle-managed files. ASM automatically assigns filenames when files are created, and automatically deletes files when they are no longer needed.

What is ASM instance in Oracle?
The ASM functionality is controlled by an ASM instance. This is not a full database instance, just the memory structures and as such is very small and lightweight.

Characteristics of Oracle ASM instance
--------------------------------------
1. do not have controlfile and datafiles, do not have online redo logs

2. do have init.ora and a passwordfile
3. for connecting remotely, create passwordfile and set following in init.ora remote_login_passwordfile=exclusive create a password file:
$ORACLE_HOME/bin/orapwd file=orapw+ASM1 password=yourpw entries=10
4. ASM instance can not be in open status as there are not datafiles. Can be in mount (although there is no controlfile) and nomount status. When in mount status, database can use the diskgroup. The mount status actually means mount disk groups.

What are ASM Background Processes in Oracle?Both an Oracle ASM instance and an Oracle Database instance are built on the same technology. Like a database instance, an Oracle ASM instance has memory structures (System Global Area) and background processes. Besides, Oracle ASM has a minimal performance impact on a server. Rather than mounting a database, Oracle ASM instances mount disk groups to make Oracle ASM files available to database instances.

There are at least two new background processes added for an ASM instance:

ASM Instance Background Processes:
---------------------------------
ARBx (ASM) Rebalance working processARBn performs the actual rebalance data extent movements in an Automatic Storage Management instance. There can be many of these processes running at a time, named ARB0, ARB1, and so on.These processes are managed by the RBAL process. The number of ARBx processes invoked is directly influenced by the asm_power_limit parameter.

RBAL (Re-balancer) RBAL runs in both database and ASM instances. In the database instance, it does a global open of ASM disks. In an ASM instance, it also coordinates rebalance activity for disk groups.RBAL, which coordinates rebalance activities for disk resources controlled by ASM.

Database Instance ASM Background Processes:
------------------------------------------In the database instances, there are three background process to support ASM, namely:

ASMB, this process contact CSS using the group name and acquires the associated ASM connect string. The connect string is subsequently used to connect to the ASM instance.

RBAL, which performs global opens on all disks in the disk group.A global open means that more than one database instance can be accessing the ASM disks at a time.

O00x, a group slave processes, with a numeric sequence starting at 000.

What are the components of components of ASM are disk groups?
The main components of ASM are disk groups, each of which comprise of several physical disks that are controlled as a single unit. The physical disks are known as ASM disks, while the files that reside on the disks are know as ASM files. The locations and names for the files are controlled by ASM, but user-friendly aliases and directory structures can be defined for ease of reference.

Failure groups are defined within a disk group to support the required level of redundancy. For two-way mirroring you would expect a disk group to contain two failure groups so individual files are written to two locations.

What are ASM instance initialization parameters?
INSTANCE_TYPE - Set to ASM or RDBMS depending on the instance type. The default is RDBMS.

DB_UNIQUE_NAME - Specifies a globally unique name for the database. This defaults to +ASM but must be altered if you intend to run multiple ASM instances.

ASM_POWER_LIMIT -The maximum power for a rebalancing operation on an ASM instance. The valid values range from 1 to 11, with 1 being the default. The higher the limit the more resources are allocated resulting in faster rebalancing operations. This value is also used as the default when the POWER clause is omitted from a rebalance operation.

ASM_DISKGROUPS - The list of disk groups that should be mounted by an ASM instance during instance startup, or by the ALTER DISKGROUP ALL MOUNT statement. ASM configuration changes are automatically reflected in this parameter.

ASM_DISKSTRING - Specifies a value that can be used to limit the disks considered for discovery. Altering the default value may improve the speed of disk group mount time and the speed of adding a disk to a disk group. Changing the parameter to a value which prevents the discovery of already mounted disks results in an error. The default value is NULL allowing all suitable disks to be considered.

Advantages of ASM in Oracle?
Provides automatic load balancing over all the available disks, thus reducing hot spots in the file system

Prevents fragmentation of disks, so you don't need to manually relocate data to tune I/O performance

Adding disks is straight forward - ASM automatically performs online disk reorganization when you add or remove storage

Uses redundancy features available in intelligent storage arrays

The storage system can store all types of database files

Using disk group makes configuration easier, as files are placed into disk groups

ASM provides stripping and mirroring (fine and coarse gain - see below)

ASM and non-ASM oracle files can coexist

Striping—ASM spreads data evenly across all disks in a disk group to optimize performance and utilization. This even distribution of database files eliminates the need for regular monitoring and I/O performance tuning.

For example, if there are six disks in a disk group, pieces of each ASM file are written to all six disks. These pieces come in 1 MB chunks known as extents. When a database file is created, it is striped (divided into extents and distributed) across the six disks, and allocated disk space on all six disks grows evenly. When reading the file, file extents are read from all six disks in parallel, greatly increasing performance.

Mirroring—ASM can increase availability by optionally mirroring any file. ASM mirrors at the file level, unlike operating system mirroring, which mirrors at the disk level. Mirroring means keeping redundant copies, or mirrored copies, of each extent of the file, to help avoid data loss caused by disk failures. The mirrored copy of each file extent is always kept on a different disk from the original copy. If a disk fails, ASM can continue to access affected files by accessing mirrored copies on the surviving disks in the disk group.

ASM supports 2-way mirroring, where each file extent gets one mirrored copy, and 3-way mirroring, where each file extent gets two mirrored copies.

Online storage reconfiguration and dynamic rebalancing—ASM permits you to add or remove disks from your disk storage system while the database is operating. When you add a disk, ASM automatically redistributes the data so that it is evenly spread across all disks in the disk group, including the new disk. This redistribution is known as rebalancing. It is done in the background and with minimal impact to database performance. When you request to remove a disk, ASM first rebalances by evenly relocating all file extents from the disk being removed to the other disks in the disk group.

Managed file creation and deletion—ASM further reduces administration tasks by enabling files stored in ASM disk groups to be Oracle-managed files. ASM automatically assigns filenames when files are created, and automatically deletes files when they are no longer needed.

Why should we use separate ASM home?
ASM should be installed separately from the database software in its own ORACLE_HOME directory. This will allow you the flexibility to patch and upgrade ASM and the database software independently.

How many ASM instances should one have?
Several databases can share a single ASM instance. So, although one can create multiple ASM instances on a single system, normal configurations should have one and only one ASM instance per system.

For clustered systems, create one ASM instance per node (called +ASM1, +ASM2, etc).

How many diskgroups should one have?
Generally speaking one should have only one disk group for all database files - and, optionally a second for recovery files (see FRA).

Data with different storage characteristics should be stored in different disk groups. Each disk group can have different redundancy (mirroring) settings (high, normal and external), different fail-groups, etc. However, it is generally not necessary to create many disk groups with the same storage characteristics (i.e. +DATA1, +DATA2, etc. all on the same type of disks).

To get started, create 2 disk groups - one for data and one for recovery files. Here is an example:

CREATE DISKGROUP data EXTERNAL REDUNDANCY DISK '/dev/d1', '/dev/d2', '/dev/d3', ....;
CREATE DISKGROUP recover EXTERNAL REDUNDANCY DISK '/dev/d10', '/dev/d11', '/dev/d12', ....;

Here is an example how you can enable automatic file management with such a setup:

ALTER SYSTEM SET db_create_file_dest = '+DATA' SCOPE=SPFILE;
ALTER SYSTEM SET db_recovery_file_dest = '+RECOVER' SCOPE=SPFILE;

You may also decide to introduce additional disk groups - for example, if you decide to put historic data on low cost disks, or if you want ASM to mirror critical data across 2 storage cabinets.

What is ASM Rebalancing?
The rebalancing speed is controlled by the ASM_POWER_LIMIT initialization parameter. Setting it to 0 will disable disk rebalancing.

ALTER DISKGROUP data REBALANCE POWER 11;

What happens when an Oracle ASM diskgroup is created?
When an ASM diskgroup is created, a hierarchialfilesystem structure is created.

How does this filesystem structure appear?
Oracle ASM diskgroup'sfilesystem structure is similar to UNIX filesystem hierarchy or Windows filesystem hierarchy.

Where are the Oracle ASM files stored?
Oracle ASM files are stored within the Oracle ASM diskgroup. If we dig into internals, oracle ASM files are stored within the Oracle ASM filesystem structures.

How are the Oracle ASM files stored within the Oracle ASM filesystem structure?
Oralce ASM files are stored within the Oracle ASM filesystem structures as objects that RDBMS instances/Oracle database instance access. RDBMS/Oracle instance treats the Oracle ASM files as standard filesystem files.

What are the Oracle ASM files that are stored within the Oracle ASM file hierarchy?
Files stored in Oracle ASM diskgroup/Oracl ASM filestructures include:
1) Datafile
2) Controlfiles
3) Server Parameter Files(SPFILE)
4) Redo Log files

What happens when you create a file/database file in ASM?What commands do you use to create database files?
Some common commands used for creating database files are :
1) Create tabespace
2) Add Datafile
3) Add Logfile
For example,
SQL> CREATE TABLESPACE TS1 DATAFILE '+DATA1' SIZE 10GB;
Above command creates a datafile in DATA1 diskgroup How can you access a databasefile in ASM diskgroup under RDBMS?
Once the ASM file is created in ASM diskgroup, a filename is generated. This file is now visible to the user via the standard RDBMS view V$DATAFILE. What will be the syntax of ASM filenames?
ASM filename syntax is as follows:
+diskgroup_name/database_name/database_file_type/tag_name.file_number.incarnation
where,
+diskgroup_name - Name of the diskgroup that contains this file database_name - Name of the database that contains this file datafile - Can be one among 20 different ASM file types tag_name - corresponds to tablespace name for datafiles, groupnumber for redo log files file_number - file_number in ASM instance is used to correlate filenames in database instance incarnation_number - It is derived from the timestamp. IT is used to provide uniqueness

What is an incarnation number?
An incarnation number is a part of ASM filename syntax. It is derived from the timestamp. Once the file is created, its incarnation number doesnot change.

What is the use of an incarnation number in Oracle ASM filename?
Incarnation number distinguishes between a new file that has been created using the same file number and another file that has been deleted

ASM's SPFile will be residing inside ASM itself. This could be found out in number of ways, looking at the alert log of ASM when ASM starts
Machine: x86_64
Using parameter settings in server-side spfile +DATA/asm/asmparameterfile/registry.253.766260991
System parameters with non-default values: large_pool_size = 12M instance_type = "asm" remote_login_passwordfile= "EXCLUSIVE" asm_diskgroups = "FLASH" asm_diskgroups = "DATA" asm_power_limit = 1 diagnostic_dest = "/opt/app/oracle"
Or using the asmcmd's spget command which shows the spfile location registered with GnP profile
ASMCMD> spget
+DATA/asm/asmparameterfile/registry.253.766260991

1. What is the use of ASM (or) Why ASM preferred over filesystem?
ASM provides striping and mirroring.

2. What are the init parameters related to ASM?
INSTANCE_TYPE = ASM
ASM_POWER_LIMIT = 11
ASM_DISKSTRING = '/dev/rdsk/*s2', '/dev/rdsk/c1*'
ASM_DISKGROUPS = DG_DATA, DG_FRA

3. What is rebalancing (or) what is the use of ASM_POWER_LIMIT?
ASM_POWER_LIMIT is dynamic parameter, which will be useful for rebalancing the data across disks.
Value can be 1(lowest) to 11 (highest).

4. What are different types of redundancies in ASM & explain?
External redundancy,
Normal redundancy, two –way mirroring
High redundancy. Three-way mirroring

5. How to copy file to/from ASM from/to filesystem?
By using ASMCMD cp command

6. How to find out the databases, which are using the ASM instance?

ASMCMD> lsct DB_Name Status Software_Version Compatible_version Instance_Name sales CONNECTED 10.2.0.1.0 10.2.0.1.0 sales1 sales CONNECTED 10.2.0.1.0 10.2.0.1.0 sales2

SQL> select DB_NAME from V$ASM_CLIENT;

7. What are different types of striping in ASM & their differences?

Fine-grained striping
Coarse-grained striping
ASM striping has two primary purposes: * To balance loads across all of the disks in a disk group * To reduce I/O latency
Coarse-grained striping provides load balancing for disk groups while fine-grained striping reduces latency for certain file types by spreading the load more widely.
To stripe data, ASM separates files into stripes and spreads data evenly across all of the disks in a disk group. The stripes are equal in size to the effective AU. The coarse-grained stripe size is always equal to the AU size. The fine-grained stripe size always equals 128 KB; this provides lower I/O latency for small I/O operations such as redo log writes.

8. What is allocation unit and what is default value of au_size and how to change?
Every ASM disk is divided into allocation units (AU). An AU is the fundamental unit of allocation within a disk group. A file extent consists of one or more AU. An ASM file consists of one or more file extents.
CREATE DISKGROUP disk_group_2 EXTERNAL REDUNDANCY DISK '/dev/sde1' ATRRIBUTE 'au_size' = '32M';

ASMCMD> lsdg State Type Rebal Unbal Sector Block AU Total_MB Free_MB Req_mir_free_MB Usable_file_MB Offline_disks Name MOUNTED EXTERN N N 512 4096 1048576 11264 9885 0 9885 0 DISKGROUP1/ MOUNTED EXTERN N N 512 4096 1048576 10240 9906 0 9906 0 FLASH/

Select NAME, ALLOCATION_UNIT_SIZE from v$asm_diskgroup;

9. What are the background processes in ASM?
Like normal database instances ASM instance too have the usual background processes like SMON, PMON, DBWr, CKPT and LGWr. In addition to that the ASM instance also have the following background processes,

RABL- Rebalancer: It opens all the device files as part of disk discovery and coordinates the ARB processes for rebalance activity.

ARBx - Actual Rebalancer: They perform the actual rebalancing activities. The number of ARBx processes depends on the ASM_POWER_LIMIT init parameter.

ASMB - ASM Bridge: This process is used to provide information to and from the Cluster Synchronization Service (CSS) used by ASM to manage the disk resources. It is also used to update statistics and provide a heartbeat mechanism.

10. What process does the rebalancing?
RBAL, ARBn

11. How to add/remove disk to/from diskgroup?
SQL> alter diskgroup data add disk '/dev/rdisk/disk30';
Diskgroup altered.
SQL> alter diskgroup data drop disk '/dev/rdisk/disk20'

12. What is ASM in Oracle?
Oracle ASM is Oracle’s volume manager specially designed for Oracle database data. It is available since Oracle database version 10g and many improvements have been made in versions 11g release 1 and 2.
ASM offers support for Oracle RAC clusters without the requirement to install 3rd party software, such as cluster aware volume managers or filesystems.
ASM is shipped as part of the database server software (Enterprise and Standard editions) and does not cost extra money to run.
ASM simplifies administration of Oracle related files by allowing the administrator to reference disk groups rather than individual disks and files, which are managed by ASM.
The ASM functionality is an extention of the Oracle Managed Files (OMF) functionality that also includes striping and mirroring to provide balanced and secure storage. The new ASM functionality can be used in combination with existing raw and cooked file systems, along with OMF and manually managed files.
13.Advantages of ASM in Oracle?
Provides automatic load balancing over all the available disks, thus reducing hot spots in the file system
Prevents fragmentation of disks, so you don’t need to manually relocate data to tune I/O performance
Adding disks is straight forward – ASM automatically performs online disk reorganization when you add or remove storage
Uses redundancy features available in intelligent storage arrays
The storage system can store all types of database files
Using disk group makes configuration easier, as files are placed into disk groups
ASM provides stripping and mirroring (fine and coarse gain – see below)
ASM and non-ASM oracle files can coexist
Striping—ASM spreads data evenly across all disks in a disk group to optimize performance and utilization. This even distribution of database files eliminates the need for regular monitoring and I/O performance tuning.
For example, if there are six disks in a disk group, pieces of each ASM file are written to all six disks. These pieces come in 1 MB chunks known as extents. When a database file is created, it is striped (divided into extents and distributed) across the six disks, and allocated disk space on all six disks grows evenly. When reading the file, file extents are read from all six disks in parallel, greatly increasing performance.
Mirroring—ASM can increase availability by optionally mirroring any file. ASM mirrors at the file level, unlike operating system mirroring, which mirrors at the disk level. Mirroring means keeping redundant copies, or mirrored copies, of each extent of the file, to help avoid data loss caused by disk failures. The mirrored copy of each file extent is always kept on a different disk from the original copy. If a disk fails, ASM can continue to access affected files by accessing mirrored copies on the surviving disks in the disk group.
ASM supports 2-way mirroring, where each file extent gets one mirrored copy, and 3-way mirroring, where each file extent gets two mirrored copies.
Online storage reconfiguration and dynamic rebalancing—ASM permits you to add or remove disks from your disk storage system while the database is operating. When you add a disk, ASM automatically redistributes the data so that it is evenly spread across all disks in the disk group, including the new disk. This redistribution is known as rebalancing. It is done in the background and with minimal impact to database performance. When you request to remove a disk, ASM first rebalances by evenly relocating all file extents from the disk being removed to the other disks in the disk group.
Managed file creation and deletion—ASM further reduces administration tasks by enabling files stored in ASM disk groups to be Oracle-managed files. ASM automatically assigns filenames when files are created, and automatically deletes files when they are no longer needed.
What is ASM instance in Oracle?
The ASM functionality is controlled by an ASM instance. This is not a full database instance, just the memory structures and as such is very small and lightweight.
Characteristics of Oracle ASM instance
————————————–
1. do not have controlfile and datafiles, do not have online redo logs
2. do have init.ora and a passwordfile
3. for connecting remotely, create passwordfile and set following in init.ora remote_login_passwordfile=exclusive create a password file:
$ORACLE_HOME/bin/orapwd file=orapw+ASM1 password=yourpw entries=10
4. ASM instance can not be in open status as there are not datafiles. Can be in mount (although there is no controlfile) and nomount status. When in mount status, database can use the diskgroup. The mount status actually means mount disk groups.
What are ASM Background Processes in Oracle?Both an Oracle ASM instance and an Oracle Database instance are built on the same technology. Like a database instance, an Oracle ASM instance has memory structures (System Global Area) and background processes. Besides, Oracle ASM has a minimal performance impact on a server. Rather than mounting a database, Oracle ASM instances mount disk groups to make Oracle ASM files available to database instances.
There are at least two new background processes added for an ASM instance:
ASM Instance Background Processes:
———————————
ARBx (ASM) Rebalance working processARBn performs the actual rebalance data extent movements in an Automatic Storage Management instance. There can be many of these processes running at a time, named ARB0, ARB1, and so on.These processes are managed by the RBAL process. The number of ARBx processes invoked is directly influenced by the asm_power_limit parameter.
RBAL (Re-balancer) RBAL runs in both database and ASM instances. In the database instance, it does a global open of ASM disks. In an ASM instance, it also coordinates rebalance activity for disk groups.RBAL, which coordinates rebalance activities for disk resources controlled by ASM.
Database Instance ASM Background Processes:
——————————————In the database instances, there are three background process to support ASM, namely:
ASMB, this process contact CSS using the group name and acquires the associated ASM connect string. The connect string is subsequently used to connect to the ASM instance.
RBAL, which performs global opens on all disks in the disk group.A global open means that more than one database instance can be accessing the ASM disks at a time.
O00x, a group slave processes, with a numeric sequence starting at 000.
What are the components of components of ASM are disk groups?
The main components of ASM are disk groups, each of which comprise of several physical disks that are controlled as a single unit. The physical disks are known as ASM disks, while the files that reside on the disks are know as ASM files. The locations and names for the files are controlled by ASM, but user-friendly aliases and directory structures can be defined for ease of reference.
Failure groups are defined within a disk group to support the required level of redundancy. For two-way mirroring you would expect a disk group to contain two failure groups so individual files are written to two locations.
What are ASM instance initialization parameters?
INSTANCE_TYPE – Set to ASM or RDBMS depending on the instance type. The default is RDBMS.
DB_UNIQUE_NAME – Specifies a globally unique name for the database. This defaults to +ASM but must be altered if you intend to run multiple ASM instances.
ASM_POWER_LIMIT -The maximum power for a rebalancing operation on an ASM instance. The valid values range from 1 to 11, with 1 being the default. The higher the limit the more resources are allocated resulting in faster rebalancing operations. This value is also used as the default when the POWER clause is omitted from a rebalance operation.
ASM_DISKGROUPS – The list of disk groups that should be mounted by an ASM instance during instance startup, or by the ALTER DISKGROUP ALL MOUNT statement. ASM configuration changes are automatically reflected in this parameter.
ASM_DISKSTRING – Specifies a value that can be used to limit the disks considered for discovery. Altering the default value may improve the speed of disk group mount time and the speed of adding a disk to a disk group. Changing the parameter to a value which prevents the discovery of already mounted disks results in an error. The default value is NULL allowing all suitable disks to be considered.
Advantages of ASM in Oracle?
Provides automatic load balancing over all the available disks, thus reducing hot spots in the file system
Prevents fragmentation of disks, so you don’t need to manually relocate data to tune I/O performance
Adding disks is straight forward – ASM automatically performs online disk reorganization when you add or remove storage
Uses redundancy features available in intelligent storage arrays
The storage system can store all types of database files
Using disk group makes configuration easier, as files are placed into disk groups
ASM provides stripping and mirroring (fine and coarse gain – see below)
ASM and non-ASM oracle files can coexist
Striping—ASM spreads data evenly across all disks in a disk group to optimize performance and utilization. This even distribution of database files eliminates the need for regular monitoring and I/O performance tuning.
For example, if there are six disks in a disk group, pieces of each ASM file are written to all six disks. These pieces come in 1 MB chunks known as extents. When a database file is created, it is striped (divided into extents and distributed) across the six disks, and allocated disk space on all six disks grows evenly. When reading the file, file extents are read from all six disks in parallel, greatly increasing performance.
Mirroring—ASM can increase availability by optionally mirroring any file. ASM mirrors at the file level, unlike operating system mirroring, which mirrors at the disk level. Mirroring means keeping redundant copies, or mirrored copies, of each extent of the file, to help avoid data loss caused by disk failures. The mirrored copy of each file extent is always kept on a different disk from the original copy. If a disk fails, ASM can continue to access affected files by accessing mirrored copies on the surviving disks in the disk group.
ASM supports 2-way mirroring, where each file extent gets one mirrored copy, and 3-way mirroring, where each file extent gets two mirrored copies.
Online storage reconfiguration and dynamic rebalancing—ASM permits you to add or remove disks from your disk storage system while the database is operating. When you add a disk, ASM automatically redistributes the data so that it is evenly spread across all disks in the disk group, including the new disk. This redistribution is known as rebalancing. It is done in the background and with minimal impact to database performance. When you request to remove a disk, ASM first rebalances by evenly relocating all file extents from the disk being removed to the other disks in the disk group.
Managed file creation and deletion—ASM further reduces administration tasks by enabling files stored in ASM disk groups to be Oracle-managed files. ASM automatically assigns filenames when files are created, and automatically deletes files when they are no longer needed.
Why should we use separate ASM home?
ASM should be installed separately from the database software in its own ORACLE_HOME directory. This will allow you the flexibility to patch and upgrade ASM and the database software independently.
How many ASM instances should one have?
Several databases can share a single ASM instance. So, although one can create multiple ASM instances on a single system, normal configurations should have one and only one ASM instance per system.
For clustered systems, create one ASM instance per node (called +ASM1, +ASM2, etc).
How many diskgroups should one have?
Generally speaking one should have only one disk group for all database files – and, optionally a second for recovery files (see FRA).
Data with different storage characteristics should be stored in different disk groups. Each disk group can have different redundancy (mirroring) settings (high, normal and external), different fail-groups, etc. However, it is generally not necessary to create many disk groups with the same storage characteristics (i.e. +DATA1, +DATA2, etc. all on the same type of disks).
To get started, create 2 disk groups – one for data and one for recovery files. Here is an example:
CREATE DISKGROUP data EXTERNAL REDUNDANCY DISK ‘/dev/d1′, ‘/dev/d2′, ‘/dev/d3′, ….;
CREATE DISKGROUP recover EXTERNAL REDUNDANCY DISK ‘/dev/d10′, ‘/dev/d11′, ‘/dev/d12′, ….;
Here is an example how you can enable automatic file management with such a setup:
ALTER SYSTEM SET db_create_file_dest = ‘+DATA’ SCOPE=SPFILE;
ALTER SYSTEM SET db_recovery_file_dest = ‘+RECOVER’ SCOPE=SPFILE;
You may also decide to introduce additional disk groups – for example, if you decide to put historic data on low cost disks, or if you want ASM to mirror critical data across 2 storage cabinets.
What is ASM Rebalancing?
The rebalancing speed is controlled by the ASM_POWER_LIMIT initialization parameter. Setting it to 0 will disable disk rebalancing.
ALTER DISKGROUP data REBALANCE POWER 11;
What happens when an Oracle ASM diskgroup is created?
When an ASM diskgroup is created, a hierarchialfilesystem structure is created.
How does this filesystem structure appear?
Oracle ASM diskgroup’sfilesystem structure is similar to UNIX filesystem hierarchy or Windows filesystem hierarchy.
Where are the Oracle ASM files stored?
Oracle ASM files are stored within the Oracle ASM diskgroup. If we dig into internals, oracle ASM files are stored within the Oracle ASM filesystem structures.
How are the Oracle ASM files stored within the Oracle ASM filesystem structure?
Oralce ASM files are stored within the Oracle ASM filesystem structures as objects that RDBMS instances/Oracle database instance access. RDBMS/Oracle instance treats the Oracle ASM files as standard filesystem files.
What are the Oracle ASM files that are stored within the Oracle ASM file hierarchy?
Files stored in Oracle ASM diskgroup/Oracl ASM filestructures include:
1) Datafile
2) Controlfiles
3) Server Parameter Files(SPFILE)
4) Redo Log files
What happens when you create a file/database file in ASM?What commands do you use to create database files?
Some common commands used for creating database files are :
1) Create tabespace
2) Add Datafile
3) Add Logfile
For example,
SQL> CREATE TABLESPACE TS1 DATAFILE ‘+DATA1′ SIZE 10GB;
Above command creates a datafile in DATA1 diskgroup
How can you access a databasefile in ASM diskgroup under RDBMS?
Once the ASM file is created in ASM diskgroup, a filename is generated. This file is now visible to the user via the standard RDBMS view V$DATAFILE.
What will be the syntax of ASM filenames?
ASM filename syntax is as follows:
+diskgroup_name/database_name/database_file_type/tag_name.file_number.incarnation
where,
+diskgroup_name – Name of the diskgroup that contains this file database_name – Name of the database that contains this file datafile – Can be one among 20 different ASM file types tag_name – corresponds to tablespace name for datafiles, groupnumber for redo log files file_number – file_number in ASM instance is used to correlate filenames in database instance incarnation_number – It is derived from the timestamp. IT is used to provide uniqueness
What is an incarnation number?
An incarnation number is a part of ASM filename syntax. It is derived from the timestamp. Once the file is created, its incarnation number doesnot change.
What is the use of an incarnation number in Oracle ASM filename?
Incarnation number distinguishes between a new file that has been created using the same file number and another file that has been deleted
ASM’s SPFile will be residing inside ASM itself. This could be found out in number of ways, looking at the alert log of ASM when ASM starts
Machine: x86_64
Using parameter settings in server-side spfile +DATA/asm/asmparameterfile/registry.253.766260991
System parameters with non-default values: large_pool_size = 12M instance_type = “asm” remote_login_passwordfile= “EXCLUSIVE” asm_diskgroups = “FLASH” asm_diskgroups = “DATA” asm_power_limit = 1 diagnostic_dest = “/opt/app/oracle”
Or using the asmcmd’s spget command which shows the spfile location registered with GnP profile
ASMCMD> spget
+DATA/asm/asmparameterfile/registry.253.766260991

-------------------------------------------------

Oracle Patching,Cloning and Upgrade Interview Questions and Answers

When you moved oracle binary files from one ORACLE_HOME server to another server then which oracle utility will be used to make this new ORACLE_HOME usable?
Relink all.

In which months oracle release CPU patches?
JAN, APR, JUL, OCT

When we applying single Patch, can you use opatch utility?
Yes, you can use Opatch incase of single patch. The only type of patch that cannot be used with OPatch is a patchset.

Is it possible to apply OPATCH without downtime?
As you know for apply patch your database and listener must be down. When you apply OPTACH it will update your current ORACLE_HOME. Thus coming to your question to the point in fact it is not possible without or zero downtime in case of single instance but in RAC you can Apply Opatch without downtime as there will be more separate ORACLE_HOME and more separate instances (running once instance on each ORACLE_HOME).

You have collection of patch (nearly 100 patches) or patchset. How can you apply only one patch from it?
With Napply itself (by providing patch location and specific patch id) you can apply only one patch from a collection of extracted patch. For more information check the opatch util NApply –help. It will give you clear picture.
For Example: opatch util napply <patch_location> -id 9 -skip_subset -skip_duplicate
This will apply only the patch id 9 from the patch location and will skip duplicate and subset of patch installed in your ORACLE_HOME.

If both CPU and PSU are available for given version which one, you will prefer to apply?
From the above discussion it is clear once you apply the PSU then the recommended way is to apply the next PSU only. In fact, no need to apply CPU on the top of PSU as PSU contain CPU (If you apply CPU over PSU will considered you are trying to rollback the PSU and will require more effort in fact). So if you have not decided or applied any of the patches then, I will suggest you to go to use PSU patches. For more details refer: Oracle Products [ID 1430923.1], ID 1446582.1

PSU is superset of CPU then why someone choose to apply a CPU rather than a PSU?
CPUs are smaller and more focused than PSU and mostly deal with security issues. It seems to be theoretically more consecutive approach and can cause less trouble than PSU as it has less code changing in it. Thus any one who is concerned only with security fixes and not functionality fixes, CPU may be good approach.

How to Download Patches, Patchset or Opatch from metalink?

If you are using latest support.oracle.com then after login to metalink Dashboard
- Click on "Patches & Updates" tab
- On the left sidebar click on "Latest Patchsets" under "Oracle Server/Tools".
- A new window will appear.
- Just mouseover on your product in the "Latest Oracle Server/Tools Patchsets" page.
- Corresponding oracle platform version will appear. Then simply choose the patchset version and click on that.
- You will go the download page. From the download page you can also change your platform and patchset version.

REFERENCES: http://docs.oracle.com/cd/E11857_01/em.111/e12255/e_oui_appendix.htm Oracle® Universal Installer and OPatch User's Guide
11g Release 2 (11.2) for Windows and UNIX
Part Number E12255-11

What is the recent Patch applied?

What is OPatch?

How to Apply Opatch in Oracle?

1. You MUST read the Readme.txt file included in opatch file, look for any prereq. steps/ post installation steps or and DB related changes. Also, make sure that you have the correct opatch version required by this patch.
2.Make sure you have a good backup of database.
3. Make a note of all Invalid objects in the database prior to the patch.
4. Shutdown All the Oracle Processes running from that Oracle Home , including the Listener and Database instance, Management agent etc.
5. You MUST Backup your oracle Home and Inventory tar -cvf $ORACLE_HOME $ORACLE_HOME/oraInventory | gzip > Backup_Software_Version.tar.gz
6. Unzip the patch in $ORACLE_HOME/patches
7. cd to the patch direcory and do opatch -apply to apply the patch.
8. Read the output/log file to make sure there were no errors.

Patching Oracle Software with OPatch ?

opatch napply <patch_location> -skip_subset -skip_duplicate
OPatch skips duplicate patches and subset patches (patches under <patch_location> that are subsets of patches installed in the Oracle home).

What is Opactch in Oracle?

OPATCH Utility (Oracle RDBMS Patching)

1. Download the required Patch from Metalink based on OS Bit Version and DB Version.
2. Need to down the database before applying patch.
3. Unzip and Apply the Patch using ”opatch apply” command.On successfully applied of patch you will see successful message “OPatch succeeded.“, Crosscheck your patch is applied by using “opatch lsinventory” command .
4. Each patch has a unique ID, the command to rollback a patch is “opatch rollback -id <patch no.>” command.On successfully applied of patch you will see successful message “OPatch succeeded.“, Crosscheck your patch is applied by using “opatch lsinventory” command .
5. Patch file format will be like, “p<patch no.>_<db version>_<os>.zip”
6. We can check the opatch version using “opatch -version” command.
7. Generally, takes 2 minutes to apply a patch.
8. To get latest Opatch version download “patch 6880880 - latest opatch tool”, it contains OPatch directory.
9. Contents of downloaded patches will be like “etc,files directories and a README file”
10. Log file for Opatch utility can be found at $ORACLE_HOME/cfgtoollogs/opatch
11. OPatch also maintains an index of the commands executed with OPatch and the log files associated with it in the history.txt file located in the <ORACLE_HOME>/cfgtoollogs/opatch directory.
12. Starting with the 11.2.0.2 patch set, Oracle Database patch sets are full installations of the Oracle Database software. This means that you do not need to install Oracle Database 11g Release 2 (11.2.0.1) before installing Oracle Database 11g Release 2 (11.2.0.2).
13. Direct upgrade to Oracle 10g is only supported if your database is running one of the following releases: 8.0.6, 8.1.7, 9.0.1, or 9.2.0. If not, you will have to upgrade the database to one of these releases or use a different upgrade option (like export/ import).
14.Direct upgrades to 11g are possible from existing databases with versions 9.2.0.4+, 10.1.0.2+ or 10.2.0.1+. Upgrades from other versions are supported only via intermediate upgrades to a supported upgrade version. http://avdeo.com/2008/08/19/opatch-utility-oracle-rdbms-patching/ -------------------------------------------------

Oracle version 10.2.0.4.0 what does each number refers to?
Oracle version number refers:
10 – Major database release number 2 – Database Maintenance release number 0 – Application server release number 4 – Component Specific release number 0 – Platform specific release number

Types of Patches?

How to rollback a patch?

What is PSU?

What is Rolling Patch?

How to check installed Patches?

How much time will it take for Patching?

Common issues faced in Patching?

REFERENCES:
OPATCH Utility (Oracle RDBMS Patching) http://avdeo.com/2008/08/19/opatch-utility-oracle-rdbms-patching/ How to apply Database Patches http://rafioracledba.blogspot.in/search/label/Database%20Patches Critical Patch Updates, Security Alerts and Third Party Bulletin http://www.oracle.com/technetwork/topics/security/alerts-086861.html Oracle: Quick Guide to Opatch - (Oracle Database Patching utility) http://www.dbalifeline.com/content/oracle-quick-guide-opatch-oracle-database-patching-utility How to Design an Effective Patch Management Process http://www.computing.net/howtos/show/how-to-design-an-effective-patch-management-process/744.html Oracle Database 11.2.0.2 Patch Set (English) http://www.dbacomp.com.br/blog/?p=69 Apply Oracle CPUApr2010 – 9352191 for Oracle10.2.0.4 in Aix5L http://hendrydasan.com/2010/05/21/apply-oracle-cpuapr2010-9352191-for-oracle10-2-0-4-in-aix5l/ Cloning
=======
What is Cloning?

How to do take RMAN Cloning? Explain Steps?

Upgrade
=======

What is rolling upgrade?It is a new ASM feature from Database 11g.ASM instances in Oracle database 11g release(from 11.1) can be upgraded or patched using rolling upgrade feature. This enables us to patch or upgrade ASM nodes in a clustered environment without affecting database availability.During a rolling upgrade we can maintain a functional cluster while one or more of the nodes in the cluster are running in different software versions.Rolling upgrade can be used only for Oracle database 11g releases(from 11.1).

Steps to Upgrade in Oracle ?

Manual upgrade which involves the following steps:
1.Backup the database.
2.In UNIX/Linux environments, set the $ORACLE_HOME and $PATH variables to point to the new 11g Oracle home.
3.Analyze the existing instance using the "$ORACLE_HOME/rdbms/admin/utlu111i.sql" script.
4.Start the original database using the STARTUP UPGRADE command and proceed with the upgrade by running the "$ORACLE_HOME/rdbms/admin/catupgrd.sql" script.
5.Recompile invalid objects.
6.Restart the database.
7.Run the "$ORACLE_HOME/rdbms/admin/utlu111s.sql" script and check the result of the upgrade.
8.Troubleshoot any issues or abort the upgrade.

What happens when you give "STARTUP UPGRADE"?

$sqlplus "/as sysdba"
SQL> STARTUP UPGRADE

Note:
----
The UPGRADE keyword enables you to open a database based on an earlier Oracle Database release. It also restricts logons to AS SYSDBAsessions, disables system triggers, and performs additional operations that prepare the environment for the upgrade.

You might be required to use the PFILE option to specify the location of your initialization parameter file.
Once the database is started in upgrade mode, only queries on fixed views execute without errors until after the catupgrd.sql script is run. Before running catupgrd.sql, queries on any other view or the use of PL/SQL returns an error.

What is the difference between startup Upgrade and Migrate ?

startup migrate:
---------------
Used to upgrade a database till 9i.

Startup Upgrade
---------------
From 10G we are using startup upgrade to upgrade database.

What happens internally when you use startup upgrade/migrate?

It will adjust few database (init) parameters (irrespective of what you have defined) automatically to certain values in order to run upgrade scripts smoothely. in other way..it will issue few alter statements to set certain parameters which are required to complete the upgrade scripts without any issues.

REFERENCE:
---------
Oracle® Database Upgrade Guide 11g Release 2 (11.2) http://docs.oracle.com/cd/E11882_01/server.112/e23633/upgrade.htm Common issues faced in Upgrade?

Error is related to timezone file
Started database in upgrade mode and fired catupgrd.sql :

SQL> startup upgrade
ORACLE instance started.
Total System Global Area 6413680640 bytes
Fixed Size 2160112 bytes
Variable Size 1946159632 bytes
Database Buffers 4429185024 bytes
Redo Buffers 36175872 bytes
Database mounted.
Database opened.
SQL> @catupgrd.sql
DOC>#######################################################################
DOC>#######################################################################
DOC>
DOC> The first time this script is run, there should be no error messages
DOC> generated; all normal upgrade error messages are suppressed.
DOC>
DOC> If this script is being re-run after correcting some problem, then
DOC> expect the following error which is not automatically suppressed:
DOC>
DOC> ORA-00001: unique constraint () violated
DOC>#
FROM registry$database *
ERROR at line 2:
ORA-00942: table or view does not exist
This error is related to timezone file which must be version 4 for Oracle version 11g.If timezone is not version 4 than patch needs to be applied.
Query to check timezone file is:
SQL> select * from v$timezone_file;
FILENAME VERSION
———— ———- timezlrg.dat 4
SQL> select * from v$timezone_file;
FILENAME VERSION
———— ———- timezlrg.dat 4
So I had correct version.I remember applying patch before upgrade.I got lucky because patch existed for version 10.2.0.3.
If there is no patch for your Oracle versions than patch can be download for similar version and applied manually.
Instructions are below:
1. Download the identified patch.
2. Unzip the patch, and locate the 2 files timezone.dat and timezlrg.dat in the “files/oracore/zoneinfo” directory of the uncompressed patch (or from the relevant .jar file of a patchset). If there is also a readme.txt in this location then make a note of this as well.
3. Backup your existing files in $ORACLE_HOME/oracore/zoneinfo – THIS CAN BE VITAL, DO NOT SKIP.
Note:
Before going on with step 4, make sure the current files are not in use.
On Windows the files will simply refuse to be removed when the are in use.
On Unix replacing the files whilst they are in use can cause the files to become corrupt. Use the fuser command before replacing the files to make sure they are not in use.
4. Copy the 2 .dat files and possibly the readme.txt file that were found in step 2 into the $ORACLE_HOME/oracore/zoneinfo directory.
5. Restart the database (in case of installation on a database), or restart the client applications (in case of client install). Note that the database did not need to be down before the time zone files were applied, but it does need to be restarted afterwards.

http://indiandba.blogspot.in/2012/01/error-is-related-to-timezone-file.html

When you moved oracle binary files from one ORACLE_HOME server to another server then which oracle utility will be used to make this new ORACLE_HOME usable?
Relink all.
In which months oracle release CPU patches?
JAN, APR, JUL, OCT
When we applying single Patch, can you use opatch utility?
Yes, you can use Opatch incase of single patch. The only type of patch that cannot be used with OPatch is a patchset.
Is it possible to apply OPATCH without downtime?
As you know for apply patch your database and listener must be down. When you apply OPTACH it will update your current ORACLE_HOME. Thus coming to your question to the point in fact it is not possible without or zero downtime in case of single instance but in RAC you can Apply Opatch without downtime as there will be more separate ORACLE_HOME and more separate instances (running once instance on each ORACLE_HOME).
You have collection of patch (nearly 100 patches) or patchset. How can you apply only one patch from it?
With Napply itself (by providing patch location and specific patch id) you can apply only one patch from a collection of extracted patch. For more information check the opatch util NApply –help. It will give you clear picture.
For Example: opatch util napply <patch_location> -id 9 -skip_subset -skip_duplicate
This will apply only the patch id 9 from the patch location and will skip duplicate and subset of patch installed in your ORACLE_HOME.
If both CPU and PSU are available for given version which one, you will prefer to apply?
From the above discussion it is clear once you apply the PSU then the recommended way is to apply the next PSU only. In fact, no need to apply CPU on the top of PSU as PSU contain CPU (If you apply CPU over PSU will considered you are trying to rollback the PSU and will require more effort in fact). So if you have not decided or applied any of the patches then, I will suggest you to go to use PSU patches. For more details refer: Oracle Products [ID 1430923.1], ID 1446582.1
PSU is superset of CPU then why someone choose to apply a CPU rather than a PSU?
CPUs are smaller and more focused than PSU and mostly deal with security issues. It seems to be theoretically more consecutive approach and can cause less trouble than PSU as it has less code changing in it. Thus any one who is concerned only with security fixes and not functionality fixes, CPU may be good approach.
How to Download Patches, Patchset or Opatch from metalink?
If you are using latest support.oracle.com then after login to metalink Dashboard
- Click on “Patches & Updates” tab
- On the left sidebar click on “Latest Patchsets” under “Oracle Server/Tools”.
- A new window will appear.
- Just mouseover on your product in the “Latest Oracle Server/Tools Patchsets” page.
- Corresponding oracle platform version will appear. Then simply choose the patchset version and click on that.
- You will go the download page. From the download page you can also change your platform and patchset version.
REFERENCES:
http://docs.oracle.com/cd/E11857_01/em.111/e12255/e_oui_appendix.htm
Oracle® Universal Installer and OPatch User’s Guide
11g Release 2 (11.2) for Windows and UNIX
Part Number E12255-11
What is the recent Patch applied?
What is OPatch?
How to Apply Opatch in Oracle?
1. You MUST read the Readme.txt file included in opatch file, look for any prereq. steps/ post installation steps or and DB related changes. Also, make sure that you have the correct opatch version required by this patch.
2.Make sure you have a good backup of database.
3. Make a note of all Invalid objects in the database prior to the patch.
4. Shutdown All the Oracle Processes running from that Oracle Home , including the Listener and Database instance, Management agent etc.
5. You MUST Backup your oracle Home and Inventory tar -cvf $ORACLE_HOME $ORACLE_HOME/oraInventory | gzip > Backup_Software_Version.tar.gz
6. Unzip the patch in $ORACLE_HOME/patches
7. cd to the patch direcory and do opatch -apply to apply the patch.
8. Read the output/log file to make sure there were no errors.
Patching Oracle Software with OPatch ? opatch napply <patch_location> -skip_subset -skip_duplicate
OPatch skips duplicate patches and subset patches (patches under <patch_location> that are subsets of patches installed in the Oracle home).
What is Opactch in Oracle?
OPATCH Utility (Oracle RDBMS Patching)
1. Download the required Patch from Metalink based on OS Bit Version and DB Version.
2. Need to down the database before applying patch.
3. Unzip and Apply the Patch using ”opatch apply” command.On successfully applied of patch you will see successful message “OPatch succeeded.“, Crosscheck your patch is applied by using “opatch lsinventory” command .
4. Each patch has a unique ID, the command to rollback a patch is “opatch rollback -id <patch no.>” command.On successfully applied of patch you will see successful message “OPatch succeeded.“, Crosscheck your patch is applied by using “opatch lsinventory” command .
5. Patch file format will be like, “p<patch no.>_<db version>_<os>.zip”
6. We can check the opatch version using “opatch -version” command.
7. Generally, takes 2 minutes to apply a patch.
8. To get latest Opatch version download “patch 6880880 – latest opatch tool”, it contains OPatch directory.
9. Contents of downloaded patches will be like “etc,files directories and a README file”
10. Log file for Opatch utility can be found at $ORACLE_HOME/cfgtoollogs/opatch
11. OPatch also maintains an index of the commands executed with OPatch and the log files associated with it in the history.txt file located in the <ORACLE_HOME>/cfgtoollogs/opatch directory.
12. Starting with the 11.2.0.2 patch set, Oracle Database patch sets are full installations of the Oracle Database software. This means that you do not need to install Oracle Database 11g Release 2 (11.2.0.1) before installing Oracle Database 11g Release 2 (11.2.0.2).
13. Direct upgrade to Oracle 10g is only supported if your database is running one of the following releases: 8.0.6, 8.1.7, 9.0.1, or 9.2.0. If not, you will have to upgrade the database to one of these releases or use a different upgrade option (like export/ import).
14.Direct upgrades to 11g are possible from existing databases with versions 9.2.0.4+, 10.1.0.2+ or 10.2.0.1+. Upgrades from other versions are supported only via intermediate upgrades to a supported upgrade version. http://avdeo.com/2008/08/19/opatch-utility-oracle-rdbms-patching/ Oracle version 10.2.0.4.0 what does each number refers to?
Oracle version number refers:
10 – Major database release number
2 – Database Maintenance release number
0 – Application server release number
4 – Component Specific release number
0 – Platform specific release number

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Oracle Backup and Recovery Interview Questions and Answers

How would you decide your backup strategy and timing for backup?
In fact backup strategy is purely depends upon your organization business need.
If no downtime then database must be run on archivelog mode and you have to take frequently or daily backup.
If sufficient downtime is there and loss of data would not affect your business then you can run your database in noarchivelog mode and backup can be taken in-frequently or weekly or monthly.
In most of the case in an organization when no downtime then frequent inconsistent backup needed (daily backup), multiplex online redo log files (multiple copies), different location for redo log files, database must run in archivelog mode and dataguard can be implemented for extra bit of protection.

What is difference between Restoring and Recovery of database?
Restoring means copying the database object from the backup media to the destination where actually it is required whereas recovery means to apply the database object copied earlier (roll forward) in order to bring the database into consistent state.

What is the difference between complete and incomplete recovery?
An incomplete database recovery is a recovery that it does not reach to the point of failure. The recovery can be either point of time or particular SCN or Particular archive log specially incase of missing archive log or redolog failure where as a complete recovery recovers to the point of failure possibly when having all archive log backup.

What is the benefit of running the DB in archivelog mode over no archivelog mode?
When a database is in no archivelog mode whenever log switch happens there will be a loss of some redoes log information in order to avoid this, redo logs must be archived. This can be achieved by configuring the database in archivelog mode.

If an oracle database is crashed? How would you recover that transaction which is not in backup?
If the database is in archivelog we can recover that transaction otherwise we cannot recover that transaction which is not in backup.

What is the difference between HOTBACKUP and RMAN backup?
For hotbackup we have to put database in begin backup mode, then take backup where as RMAN would not put database in begin backup mode. RMAN is faster can perform incremental (changes only) backup, and does not place tablespace in hotbackup mode.

Can we use Same target database as Catalog database?
No, the recovery catalog should not reside in the target database (database to be backed up) because the database can not be recovered in the mounted state.
Incremental backup levels:
Level 0 – full backup that can be used for subsequent incrementals
RMAN> backup incremental level 0 database;
Differential Level 1–only the blocks that have changed since the last backup (whether it is level 0 or level 1)
RMAN> backup incremental level 1 differential database;
Cumulative Level 1 – all changes since the last level 0 incremental backup
RMAN> backup incremental level 1 cumulative database;
A full backup cannot be used for a cumulative level 1 backup.
A cumulative level 1 backup must be done on top of an incremental level 0 backup.
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Why RMAN incremental backup fails even though full backup exists?
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If you have taken the RMAN full backup using the command ‘Backup database’, where as a level 0 backup is physically identical to a full backup. The only difference is that the level 0 backup is recorded as an incremental backup in the RMAN repository so it can be used as the parent for a level 1 backup. Simply the ‘full backup without level 0’ can not be considered as a parent backup from which you can take level 1 backup.

Can we perform RMAN level 1 backup without level 0?
If no level 0 is available, then the behavior depends upon the compatibility mode setting (oracle version).
If the compatibility mode less than 10.0.0, RMAN generates a level 0 backup of files contents at the time of backup.
If the compatibility is greater than 10.0.0, RMAN copies all block changes since the file was created, and stores the results as level 1 backup. How to put Manual/User managed backup in RMAN?In case of recovery catalog, you can put by using catalog command:
RMAN> CATALOG START WITH ‘/oracle/backup.ctl’;

How to check RMAN version in oracle?If you want to check RMAN catalog version then use the below query from SQL*plus
SQL> Select * from rcver;

What happens actually in case of instance Recovery?While Oracle instance fails, Oracle performs an Instance Recovery when the associated database is being re-started. Instance recovery occurs in 2 steps:
Cache recovery: Changes being made to a database are recorded in the database buffer cache as well as redo log files simultaneously. When there are enough data in the database buffer cache, they are written to data files. If an Oracle instance fails before these data are written to data files, Oracle uses online redo log files to recover the lost data when the associated database is re-started. This process is called cache recovery.
Transaction recovery: When a transaction modifies data in a database (the before image of the modified data is stored in an undo segment which is used to restore the original values in case the transaction is rolled back). At the time of an instance failure, the database may have uncommitted transactions. It is possible that changes made by these uncommitted transactions have gotten saved in data files. To maintain read consistency, Oracle rolls back all uncommitted transactions when the associated database is re-started. Oracle uses the undo data stored in undo segments to accomplish this. This process is called transaction recovery.

My Database has Level 1 backup, tell me what are all backed up ? with Example?

Database is UP and has taken Level 0 backup, is the backup taken is Consistent or Inconsistent?

How do you say a backup is Consistent or Inconsistent, Oracle Terminology?

Can we take backup when the Database is down?

If i have a RMAN full backup Level 0 of Sun @9PM, on Mon 9PM taken incremental Level 1 backup.What type of backup do you get and what is actually backedup?

If i have a RMAN full backup of Sun @9PM, on Mon 9PM taken incremental Level 1 backup.On Tuesday Database Crashed.What type of backup do you get and what is actually backedup?

There is no Backup available, Can we take a Level 1 backup?

A table got dropped between 9AM - 11AM how to get the Table backup using RMAN,
DB size 500GB available mount point space for table recovery is 15GB?

Sys Admin has changed the time from 10:00 AM to 9:30 AM, table dropped, How do you recover the Table?

A DATAFILE is corrupted and there is no backup, How to recover the datafile?

All Controlfiles are corrupted, How to recover the controlfile?

How would you decide your backup strategy and timing for backup?In fact backup strategy is purely depends upon your organization business need.
If no downtime then database must be run on archivelog mode and you have to take frequently or daily backup.
If sufficient downtime is there and loss of data would not affect your business then you can run your database in noarchivelog mode and backup can be taken in-frequently or weekly or monthly.
In most of the case in an organization when no downtime then frequent inconsistent backup needed (daily backup), multiplex online redo log files (multiple copies), different location for redo log files, database must run in archivelog mode and dataguard can be implemented for extra bit of protection.
What is difference between Restoring and Recovery of database?
Restoring means copying the database object from the backup media to the destination where actually it is required where as recovery means to apply the database object copied earlier (roll forward) in order to bring the database into consistent state.
What is the difference between complete and incomplete recovery?An incomplete database recovery is a recovery that it does not reach to the point of failure. The recovery can be either point of time or particular SCN or Particular archive log specially incase of missing archive log or redolog failure where as a complete recovery recovers to the point of failure possibly when having all archive log backup.
What is the benefit of running the DB in archivelog mode over no archivelog mode?
When a database is in no archivelog mode whenever log switch happens there will be a loss of some redoes log information in order to avoid this, redo logs must be archived. This can be achieved by configuring the database in archivelog mode.
If an oracle database is crashed? How would you recover that transaction which is not in backup?If the database is in archivelog we can recover that transaction otherwise we cannot recover that transaction which is not in backup.
What is the difference between HOTBACKUP and RMAN backup?
For hotbackup we have to put database in begin backup mode, then take backup where as RMAN would not put database in begin backup mode. RMAN is faster can perform incremental (changes only) backup, and does not place tablespace in hotbackup mode.
Can we use Same target database as Catalog database?
No, the recovery catalog should not reside in the target database (database to be backed up) because the database can not be recovered in the mounted state.
Incremental backup levels:
Level 0 – full backup that can be used for subsequent incrementals
RMAN> backup incremental level 0 database;
Differential Level 1–only the blocks that have changed since the last backup (whether it is level 0 or level 1)
RMAN> backup incremental level 1 differential database;
Cumulative Level 1 – all changes since the last level 0 incremental backup
RMAN> backup incremental level 1 cumulative database;
A full backup cannot be used for a cumulative level 1 backup.
A cumulative level 1 backup must be done on top of an incremental level 0 backup.
Why RMAN incremental backup fails even though full backup exists?If you have taken the RMAN full backup using the command ‘Backup database’, where as a level 0 backup is physically identical to a full backup. The only difference is that the level 0 backup is recorded as an incremental backup in the RMAN repository so it can be used as the parent for a level 1 backup. Simply the ‘full backup without level 0’ can not be considered as a parent backup from which you can take level 1 backup.
Can we perform RMAN level 1 backup without level 0?If no level 0 is available, then the behavior depends upon the compatibility mode setting (oracle version).
If the compatibility mode less than 10.0.0, RMAN generates a level 0 backup of files contents at the time of backup.
If the compatibility is greater than 10.0.0, RMAN copies all block changes since the file was created, and stores the results as level 1 backup.
How to put Manual/User managed backup in RMAN?In case of recovery catalog, you can put by using catalog command:
RMAN> CATALOG START WITH ‘/oracle/backup.ctl’;
How to check RMAN version in oracle?If you want to check RMAN catalog version then use the below query from SQL*plus
SQL> Select * from rcver;
What happens actually in case of instance Recovery?While Oracle instance fails, Oracle performs an Instance Recovery when the associated database is being re-started. Instance recovery occurs in 2 steps:
Cache recovery: Changes being made to a database are recorded in the database buffer cache as well as redo log files simultaneously. When there are enough data in the database buffer cache, they are written to data files. If an Oracle instance fails before these data are written to data files, Oracle uses online redo log files to recover the lost data when the associated database is re-started. This process is called cache recovery.
Transaction recovery: When a transaction modifies data in a database (the before image of the modified data is stored in an undo segment which is used to restore the original values in case the transaction is rolled back). At the time of an instance failure, the database may have uncommitted transactions. It is possible that changes made by these uncommitted transactions have gotten saved in data files. To maintain read consistency, Oracle rolls back all uncommitted transactions when the associated database is re-started. Oracle uses the undo data stored in undo segments to accomplish this. This process is called transaction recovery.
Oracle RMAN Interview Questions and Answers

1. Difference between catalog and nocatalog?
CATALOG is used when you use a repository database as catalog. NOCATALOG is used when you used the controlfile to register your backup information. Default in NOCATALOG. However I suggest you to have a separate database catalog on another machine.
2. Difference between using recovery catalog and control file?
When new incarnation happens, the old backup information in control file will be lost. It will be preserved in recovery catalog.
In recovery catalog, we can store scripts.
Recovery catalog is central and can have information of many databases.

3. Can we use same target database as catalog?
No. The recovery catalog should not reside in the target database (database to be backed up), because the database can't be recovered in the mounted state.

4. How do u know how much RMAN task has been completed?
By querying v$rman_status or v$session_longops

5. From where list & report commands will get input?
List & Report command queries the RMAN repository (recovery catalog or control file) and produces a record of its contents. Both the commands command quering v$ and recovery catalog views. V$BACKUP_FILES or many of the recovery catalog views such asRC_DATAFILE_COPY or RC_ARCHIVED_LOG.

6. Command to delete archive logs older than 7days?
RMAN> delete archivelog all completed before sysdate-7;

7. How many days backup, by default RMAN stores?
1 , as per Retention policy

8. What is the use of crosscheck command in RMAN?
Crosscheck will be useful to check whether the catalog information is intact with OS level information.
This command only updates repository records with the status of the backups.
e.g. If user removes archived logs from disk with an operating system command, the repository still indicates that the logs are on disk, when in fact they are not.

9. What are the differences between crosscheck and validate commands?
Crosscheck command is to verify the status of backups and copies recorded in the RMAN repository against media such as disk or tape. The crosscheck command only processes files created on the same device type as the channel running crosscheck.

Validate command is to examine a backup set and report whether it can be restored. RMAN scans all of the backup pieces in the specified backup sets and looks at the checksum to verify that the contents are intact so that backup can be successfully restored if necessary.

10. Which is one is good, differential (incremental) backup or cumulative (incremental) backup?
A differential backup, which backs up all blocks changed after the most recent incremental backup at level 1 or 0
A cumulative backup, which backs up all blocks changed after the most recent incremental backup at level 0

11. What is Level 0, Level 1 backup?
A level 0 incremental backup, which is the base for subsequent incremental backups, copies all blocks containing data, backing the datafile up into a backup set just as a full backup would. A level 1 incremental backup can be either of the following types:
A differential backup, which backs up all blocks changed after the most recent incremental backup at level 1 or 0
A cumulative backup, which backs up all blocks changed after the most recent incremental backup at level 0

12. Can we perform level 1 backup without level 0 backup?
If no level 0 backup is available, then the behavior depends upon the compatibility mode setting. If compatibility < 10.0.0, RMAN generates a level 0 backup of the file contents at the time of the backup. If compatibility is >= 10.0.0, RMAN copies all blocks changed since the file was created, and stores the results as a level 1 backup. In other words, the SCN at the time the incremental backup is taken is the file creation SCN.

13. Will RMAN put the database/tablespace/datafile in backup mode?
Nope.

14. What is snapshot control file?
The snapshot control file is a copy of a database control file created in an operating system-specific location by RMAN. RMAN creates the snapshot control file so that it has a consistent version of a control file to use when either resynchronizing the recovery catalog or backing up the control file.
15. What is the difference between backup set and backup piece?
Backup set is logical and backup piece is physical.

16. RMAN command to backup for creating standby database?
RMAN> duplicate target database to standby database ....

17. How to do cloning by using RMAN?
RMAN> duplicate target database …

18. You loss one datafile and DB is running in ARCHIVELOG mode. You have full database backup of 1 week/day old and don’t have backup of this (newly created) datafile. How do you restore/recover file? create the datafile and recover that datafile.
SQL> alter database create datafile ‘…path..’ size n;
RMAN> recover datafile file_id;

19. What is obsolete backup & expired backup?
A status of "expired" means that the backup piece or backup set is not found in the backup destination.
A status of "obsolete" means the backup piece is still available, but it is no longer needed. The backup piece is no longer needed since RMAN has been configured to no longer need this piece after so many days have elapsed, or so many backups have been performed.

20. What is the difference between hot backup & RMAN backup?
For hot backup, we have to put database in begin backup mode, then take backup.
RMAN won’t put database in backup mode.

21. How to put manual/user-managed backup in RMAN (recovery catalog)?
By using catalog command.
RMAN> CATALOG START WITH '/tmp/backup.ctl';

22. What are new features in Oracle 11g RMAN?
Oracle 11g introduced many exciting new features in Recovery Manager (RMAN). Lets start using these new features and benefit from it.

• RMAN Proactive health checks: - Now you can proactively check database block corruptions using VALIDATE DATABASE
RMAN > VALIDATE DATABASE;

You can also run the proactive check on a datafile, tablespace or block.
RMAN > VALIDATE DATAFILE 1 BLOCK 10;
RMAN > VALIDATE TABLESAPCE users;

• Database Recovery Advisor : – The data recovery advisor automatically diagnoses the corruptions and loss of data on disk and determines the corrective repair options.

The LIST FAILURE command displays any failures with priority of CRITICAL or HIGH in order of importance
RMAN> LIST FAILURE

The ADVISE FAILURE command provides repair advice for failures listed by LIST FAILURE
RMAN > ADVICE FAILURE

The REPAIR FAILURE command applies the repair scripts advised by the ADVISE FAILURE command.
RMAN>REPAIR FAILURE

You can also use PREVIEW command to see the contents of the repair before proceeding to actual repair
RMAN>REPAIR FAILURE PREVIEW

• Faster Backup Compression: The ZLIB compression is faster than original B2ZIP compression with less CPU resources

Use below command for ZLIB compression
RMAN> configure compression algorithm 'ZLIB' ;

Use below command to change compression to BZIP2
RMAN> configure compression algorithm 'bzip2';

• More backup Comcodession Choices (11gR2 only): Now we have different types of comcodession levels, i.e. LOW, MEDIUM and HIGHT and with CPU resource usage from least to highest.

Here is the example
RMAN> configure comcodession algorithm ‘medium’;

• RMAN Backups to Cloud: Now you can set your RMAN backup destination to Cloud. Amazon provides cloud computing service, but you need to use specially developed media management library.

• RMAN UNDO bypass: The RMAN backup command no longer backs up the UNDO data that is not needed for recovery. Prior to Oracle 11g, all UNDO transactions that were already committed also backed up. This backup undo optimization minimizes the backup time and storage.

• Duplicate Database from Backup (11gR2 only): Prior 11g, In order to duplicate a database using DUPLICATE TARGET DATABASE command you need connect to target database. In case if target database is down you cannot able to duplicate. From 11g, you can able to duplicate the database without connecting to target database, make sure that you have backups available on duplicate site.

Here is the example for duplicate database connect auxiliary sys/xxxx@dup connect catalog rman/xxx@rmancat duplicate database 'PRD' to DUP' until time "to_date('01/01/11 10:00:00','mm/dd/yy hh24:mi:ss')" db_file_name_convert =( “/dbs1/oradata/PRD","/dbs2/oradata/DUP") backup location '/rman_backup' ;

Duplicate Database options
-NOREDO – Using this option no archivelogs will be applied
-UNDO_TABLESPACE – You must specify the UNDO tablesapce when you are not connected to target database.

• Set NEWNAME Flexibility while restoring Database (11gR2 only): When you are restoring database on different server with different file system structure you need to change data file path using “SET NEWNAME” command. If you have hundreds of datafiles then you need to change the path for all data files.

run
{
set newname for datafile 1 to ‘/dbs1/oradata/system01.dbf’; set newname for datafile 2 to ‘/dbs2/oradata/users01.dbf’;
---- (Some detail removed for brevity) ---- restore database;
}

From 11g, you have flexibility using a single “SET NEWNAME” clause for all datafiles in a tablespace.

run
{
set newname for tablespace DATA to '/dbs1/oradata/data%b.dbf'; set newname for tablespace INDEX to '/dbs2/oradata/index%b.dbf';
---- (Some detail removed for brevity) ----
Restore database;
}

You can also set the path for entire database using a single command. run { set newname for database to '/dbs1/oradata/%b'; restore database;
}

• TO DESTINATION Clause in BACKUP command (11gR2 only): You can specify a destination location for RMAN backups using “TO DESTINATION” clause .

RMAN> backup tablespace users to destination '/backup/rman;
You can also use this clause in ALLOCATE CHANNEL command
RMAN> run {
2> allocate channel c1 type disk to destination '/backup/rman'; backup database;
3> }

• Parallel backup of Same datafile: Now you can break the large datafiles into small sections and it reduces the backup time of large datafiles

Here is the example run { allocate channel c1 type disk format '/rman_backup1/%U'; allocate channel c2 type disk format '/rman_backup2/%U'; backup section size 100m datafile 10;
}

• Automatic Block Repair (11g R2 Only): This feature automatically repairs the blocks on primary from blocks on Physical Standby. RECOVER BLOCK enhanced to repair the blocks on Primary as soon as it detects the corruption from standby when available.

• Transported Tablespace Enhancement: Prior 11g, the transported tablespace must be in read-only mode. But from 11g onwards you can transport the tablespace both in read-only and read-write mode.

• Virtual Private Catalog: The virtual catalogs are created within in same RMAN Catalog. Prior to 11g, we have only one catalog and catalog owner can able to see repository information for all databases. From 11g, you can separate the catalog database access across the departments/groups (for ex, Manufacturing, IT…etc.) using virtual catalogs feature to maximize the security.

Create a separate user for IT department to grant catalog access
SQL> create user it_user identified by xxxxx quota unlimited on users;
SQL> grant recovery_catalog_owner to it_user;

Grant catalog access on “itdb1” to virtual catalog owner “it_user”
$ rman target=/ rcvcat rman/rman@rmancat
RMAN> grant catalog for database itdb1 to it_user;

Now connect using the virtual catalog owner “it_user” and create virtual catalog
$ rman target=/ rcvcat ituser/xxxx@rmancat
RMAN> create virtual catalog;

• Merging RMAN Catalogs: If you have operations across different regions and maintaining different catalogs for each state and want to merge then you can use merge catalog feature without re-registering the databases in new catalog.
In below example we are importing rmancat2 into rmancat1
$ rman target=/ rcvcat rman/rman@rmancat1
RMAN> import catalog rman/rman@rmancat2;

• GUI interface for RMAN: Now you can use RMAN functionality through a GUI iFrom Enterprise manager

•Archive log Deletion Policy Enhancements: The archive log deletion policy has been extended in 11g for greater flexibility and protection for Dataguard environments.

Oracle 10g Syntax.
CONFIGURE ARCHIVELOG DELETION POLICY {CLEAR | TO {APPLIED ON STANDBY | NONE}}

Oracle 11g Syntax.
ARCHIVELOG DELETION POLICY {CLEAR | TO {APPLIED ON [ALL] STANDBY |BACKED UP integer TIMES TO DEVICE TYPE deviceSpecifier |NONE | SHIPPED TO [ALL] STANDBY}[ {APPLIED ON [ALL] STANDBY | BACKED UP integer TIMES TO DEVICE TYPE deviceSpecifier |NONE | SHIPPED TO [ALL] STANDBY}]...}

23. What is the difference between auxiliary channel and maintenance channel?
An RMAN channel represents one stream of data to a device type, and corresponds to one server session. Most backup and recovery commands in RMAN are executed by server sessions. each channel establishes a connection from the RMAN client to a target or auxiliary database instance by starting a server session on the instance. The server session performs the backup, restore, and recovery.

Oracle Performance Tuning Interview Questions and Answers

Application user is complaining the database is slow.How would you find the performance issue of SQL queries?
High performance is common expectation for end user, in fact the database is never slow or fast in most of the case session connected to the database slow down when they receives unexpected hit. Thus to solve this issue you need to find those unexpected hit. To know exactly what the session is doing join your query v$session with v$session_wait.
SELECT NVL(s.username,’(oracle)’) as username,s.sid,s.serial#,sw.event,sw.wait_time, sw.seconds_in_wait, sw.state FROM v$session_wait sw,v$session s
WHERE s.sid=sw.sid and s.username= ‘&username’ORDER BY sw.seconds_in_wait DESC;
1.Check the events that are waiting for something.
2.Try to find out the objects locks for that particular session.
3.Locking is not only the cause to effects the performance. Disk I/O contention is another case. When a session retrieves data from the database datafiles on disk to the buffer cache, it has to wait until the disk sends the data. The wait event shows up for the session as “db file sequential read” (for index scan) or “db file scattered read” (for full table scan).When you see the event, you know that the session is waiting for I/O from the disk to complete. To improve session performance, you have to reduce that waiting period. The exact step depends on specific situation, but the first technique “reducing the number of blocks retrieved by a SQL statement” almost always works.Reduce the number of blocks retrieved by the SQL statement. Examine the SQL statement to see if it is doing a full-table scan when it should be using an index, if it is using a wrong index, or if it can be rewritten to reduce the amount of data it retrieves.
4.Run SQL Tuning Advisor (@$ORACLE_HOME/rdbms/admin/sqltrpt.sql) by providing SQL_ID as the input for generating the findings and recommendations.
SQL Tuning Advisor seems to be doing logical optimization mainly by checking your SQL structure and statistics.
SQL Tuning Advisor suggests indexes that might be very useful.
SQL Tuning Advisor suggests query rewrites.
SQL Tuning Advisor suggests SQL profile.
More:
1.Run TOP command in Linux to check CPU usage.
2.Run VMSTAT, SAR, PRSTAT command to get more information on CPU, memory usage and possible blocking.
3.Enable the trace file before running your queries,then check the trace file using tkprof create output file.
According to explain plan check the elapsed time for each query,then tune them respectively.
What is the use of iostat/vmstat/netstat command in Linux?
Iostat – reports on terminal, disk and tape I/O activity.
Vmstat – reports on virtual memory statistics for processes, disk, tape and CPU activity.
Netstat – reports on the contents of network data structures.
If you are getting high “Busy Buffer waits”, how can you find the reason behind it?
Buffer busy wait means that the queries are waiting for the blocks to be read into the db cache. There could be the reason when the block may be busy in the cache and session is waiting for it. It could be undo/data block or segment header wait.
Run the below two query to find out the P1, P2 and P3 of a session causing buffer busy wait then after another query by putting the above P1, P2 and P3 values.
SQL> Select p1 “File #”,p2 “Block #”,p3 “Reason Code” from v$session_wait Where event = ‘buffer busy waits’;
SQL> Select owner, segment_name, segment_type from dba_extents
Where file_id = &P1 and &P2 between block_id and block_id + blocks -1;
What to Look for in AWR Report and STATSPACK Report?
Many DBAs already know how to use STATSPACK but are not always sure what to check regularly.
Remember to separate OLTP and Batch activity when you run STATSPACK, since they usually generate different types of waits. The SQL script “spauto.sql” can be used to run STATSPACK every hour on the hour. See the script in $ORACLE_HOME/rdbms/admin/spauto.sql for more information (note that JOB_QUEUE_PROCESSES must be set > 0). Since every system is different, this is only a general list of things you should regularly check in your STATSPACK output:
¦ Top 5 wait events (timed events)
¦ Load profile
¦ Instance efficiency hit ratios
¦ Wait events
¦ Latch waits
¦ Top SQL
¦ Instance activity
¦ File I/O and segment statistics
¦ Memory allocation
¦ Buffer waits
What is the difference between DB file sequential read and DB File Scattered Read?
DB file sequential read is associated with index read where as DB File Scattered Read has to do with full table scan.
The DB file sequential read, reads block into contiguous memory and DB File scattered read gets from multiple block and scattered them into buffer cache.
Which factors are to be considered for creating index on Table? How to select column for index?
Creation of index on table depends on size of table, volume of data. If size of table is large and we need only few data for selecting or in report then we need to create index. There are some basic reason of selecting column for indexing like cardinality and frequent usage in where condition of select query. Business rule is also forcing to create index like primary key, because configuring primary key or unique key automatically create unique index.
It is important to note that creation of so many indexes would affect the performance of DML on table because in single transaction should need to perform on various index segments and table simultaneously.
Is creating index online possible?
YES. You can create and rebuild indexes online. This enables you to update base tables at the same time you are building or rebuilding indexes on that table. You can perform DML operations while the index building is taking place, but DDL operations are not allowed. Parallel execution is not supported when creating or rebuilding an index online.
CREATE INDEX emp_name ON emp (mgr, emp1, emp2, emp3) ONLINE;
How to recover password in oracle 10g?
You can query with the table user_history$. The password history is store in this table.
How can you track the password change for a user in oracle?
Oracle only tracks the date that the password will expire based on when it was latest changed. Thus listing the view DBA_USERS.EXPIRY_DATE and subtracting PASSWORD_LIFE_TIME you can determine when password was last changed. You can also check the last password change time directly from the PTIME column in USER$ table (on which DBA_USERS view is based). But If you have PASSWORD_REUSE_TIME and/or PASSWORD_REUSE_MAX set in a profile assigned to a user account then you can reference dictionary table USER_HISTORY$ for when the password was changed for this account.
SELECT user$.NAME, user$.PASSWORD, user$.ptime, user_history$.password_date
FROM SYS.user_history$, SYS.user$
WHERE user_history$.user# = user$.user#;
What is Secure External password Store (SEPS)?
Through the use of SEPS you can store password credentials for connecting to database by using a client side oracle wallet, this wallet stores signing credentials. This feature introduced since oracle 10g. Thus the application code, scheduled job, scripts no longer needed embedded username and passwords. This reduces risk because the passwords are no longer exposed and password management policies are more easily enforced without changing application code whenever username and password change.
Why we need CASCADE option with DROP USER command whenever dropping a user and why “DROP USER” commands fails when we don’t use it?
If a user having any object then ‘YES’ in that case you are not able to drop that user without using CASCADE option. The DROP USER with CASCADE option command drops user along with its all associated objects. Remember it is a DDL command after the execution of this command rollback cannot be performed.
What is the difference between Redo,Rollback and Undo?
I find there is always some confusion when talking about Redo, Rollback and Undo. They all sound like pretty much the same thing or at least pretty close.
Redo: Every Oracle database has a set of (two or more) redo log files. The redo log records all changes made to data, including both uncommitted and committed changes. In addition to the online redo logs Oracle also stores archive redo logs. All redo logs are used in recovery situations.
Rollback: More specifically rollback segments. Rollback segments store the data as it was before changes were made. This is in contrast to the redo log which is a record of the insert/update/deletes.
Undo: Rollback segments. They both are really one in the same. Undo data is stored in the undo tablespace. Undo is helpful in building a read consistent view of data.
You have more than 3 instances running on the Linux server? How can you determine which shared memory and semaphores are associated with which instance?
Oradebug is undocumented oracle supplied utility by oracle. The oradebug help command list the command available with oracle.
SQL>oradebug setmypid
SQL>oradebug ipc
SQL>oradebug tracfile_name
Why drop table is not going into Recycle bin?
If you are using SYS user to drop any table then user’s object will not go to the recyclebin as there is no recyclebin for SYSTEM tablespace, even we have already SET recycle bin parameter TRUE.
Select * from v$parameter where name = ‘recyclebin’;
Show parameter recyclebin;
Temp Tablespace is 100% FULL and there is no space available to add datafiles to increase temp tablespace. What can you do in that case to free up TEMP tablespace?
Try to close some of the idle sessions connected to the database will help you to free some TEMP space. Otherwise you can also use ‘Alter Tablespace PCTINCREASE 1’ followed by ‘Alter Tablespace PCTINCREASE 0’
What is Row Chaning and Row Migration?
Row Migration:
A row migrates when an update to that row would cause it to not fit on the block anymore (with all of the other data that exists there currently). A migration means that the entire row will move and we just leave behind the «forwarding address». So, the original block just has the rowid of the new block and the entire row is moved.
Row Chaining:
A row is too large to fit into a single database block. For example, if you use a 4KB blocksize for your database, and you need to insert a row of 8KB into it, Oracle will use 3 blocks and store the row in pieces.
Some conditions that will cause row chaining are: Tables whose rowsize exceeds the blocksize. Tables with LONG and LONG RAW columns are prone to having chained rows. Tables with more then 255 columns will have chained rows as Oracle break wide tables up into pieces.
So, instead of just having a forwarding address on one block and the data on another we have data on two or more blocks.
How to find out background processes ?
SQL> select SID,PROGRAM from v$session where TYPE=’BACKGROUND’;
SQL> select name,description from V$bgprocess;
How to findout background processes from OS:
$ ps -ef|grep ora_|grep SID
To Find and Delete bigger size and older files in Linux
–To find out files size more than 5MB find . -size +5000 -exec ls -ltr {} \;
– To **Remove** files size more than 5MB find . -size +5000k -exec rm -rf {} \;
–To find out files older than 30days find . -mtime +30 -exec ls -ltr {} \;
–To find **Remove** files older than 30days find . -mtime +30 -exec rm -rf {} \;

1. What you’ll check whenever user complains that his session/database is slow? You should be using statspack on a constant basis. Every morning, you should take a snapshot, every afternoon another, every evening, yet another. Now you have a history. You can compare a statspack from today (bad performance) with last weeks at the same time (good performance) and look for major differences. Also, people must "quantify" things. Eg: Screen 1 typically takes less then 1 second, today it is taking 60 seconds. -- Ah ha, maybe we lost an index on some of the tables surrounding screen 1, lets look at that. Are there specific components "going slow" or is the entire thing going slow. Statspack will help you identify the top sql, the big wait events, contention points, bad performance metric (eg: the soft parse ratio is my personal favorite). Also, attack this from two points - get the SA's looking at the machine, network, disks, etc. As it is now, if you don't have a history of what "good" looks like - it is REALLY REALLY hard to figure out "badness". You need to gather more information, isolate the issue if possible and go from there. TOP shows you that on some OS's (hp/ux for sure, not sure about sun) but they'll move around from cpu to cpu faster then you can keep track of them. It's not specific CPU's (processes are not bound to a cpu), it's all of them -- seeing which ones on a CPU right now isn't relevant a second from now.

2. What is the use of statistics?
The term "Oracle statistics" may refer to historical performance statistics that are kept in STATSPACK and AWR, but a more common use of the term "Oracle statistics" is about Oracle optimizer "Metadata statistics" in order to provide the cost-based SQL optimizer with the information about the nature of the tables. Oracle statistics tell you the size of the tables, the distribution of values within a columns, and other important information so that SQL statements will always generate the "best" execution plans.

3. How to generate explain plan?
EXPLAIN PLAN parses a query and records the "plan" that Oracle devises to execute it. By examining this plan, you can find out if Oracle is picking the right indexes and joining your tables in the most efficient manner. There are a few different ways to utilize Explain Plan. We will focus on using it through SQL*Plus since most Oracle programmers have access to SQL*Plus. EXPLAIN PLAN SET STATEMENT_ID = statement_id FOR your-sql-statement;

4. How to check explain plan of already ran SQLs?

5. How to find out whether the query has ran with RBO or CBO?

6. What are top 5 wait events (in AWR report) and how you will resolve them? http://satya-dba.blogspot.in/2012/10/wait-events-in-oracle-wait-events.html db file sequential read => tune indexing, tune SQL (to do less I/O), tune disks, increase buffer cache. This event is indicative of disk contention on index reads. Make sure all objects are analyzed. Redistribute I/O across disks. The wait that comes from the physical side of the database. It related to memory starvation and non selective index use. Sequential read is an index read followed by table read because it is doing index lookups which tells exactly which block to go to. db file scattered read => disk contention on full table scans. Add indexes, tune SQL, tune disks, refresh statistics, and create materialized view. Caused due to full table scans may be because of insufficient indexes or unavailability of updated statistics. db file parallel read => tune SQL, tune indexing, tune disk I/O, increase buffer cache. If you are doing a lot of partition activity then expect to see that wait even. It could be a table or index partition. db file parallel write => if you are doing a lot of partition activity then expect to see that wait even. It could be a table or index partition. db file single write => if you see this event than probably you have a lot of data files in your database.

control file sequential read control file parallel write

log file sync => committing too often, archive log generation is more. Tune applications to commit less, tune disks where redo logs exist, try using nologging/unrecoverable options, log buffer could be too large. log file switch completion => May need more log files per group. log file parallel write => Deals with flushing out the redo log buffer to disk. Disks may be too slow or have an I/O bottleneck. Look for log file contention. log buffer space => Increase LOG_BUFFER parameter or move log files to faster disks. Tune application, use NOLOGGING, and look for poor behavior that updates an entire row when only a few columns change. log file switch (checkpoint incomplete) => May indicate excessive db files or slow IO subsystem. log file switch (archiving needed) => Indicates archive files are written too slowly. redo buffer allocation retries => shows the number of times a user process waited for space in the redo log buffer. redo log space wait time => shows cumulative time (in 10s of milliseconds) waited by all processes waiting for space in the log buffer.

buffer busy waits/ read by other session => Increase DB_CACHE_SIZE. Tune SQL, tune indexing, we often see this event along with full table scans, if the SQL is inserting data, consider increasing FREELISTS and/or INITRANS, if the waits are on segment header blocks, consider increasing extent sizes. free buffer waits => insufficient buffers, process holding buffers too long or i/o subsystem is over loaded. Also check you db writes may be getting clogged up. cache buffers lru chain => Freelist issues, hot blocks. no free buffers => Insufficient buffers, dbwr contention.

latch free latch: session allocation latch: in memory undo latch => If excessive could be bug, check for your version, may have to turn off in memory undo. latch: cache buffer chains => check hot objects. latch: cache buffer handles => Freelist issues, hot blocks. direct path write => You wont see them unless you are doing some appends or data loads. direct Path reads => could happen if you are doing a lot of parallel query activity. direct path read temp or direct path write temp => this wait event shows Temp file activity (sort,hashes,temp tables, bitmap) check pga parameter or sort area or hash area parameters. You might want to increase them. library cache load lock library cache pin => if many sessions are waiting, tune shared pool, if few sessions are waiting, lock is session specific. library cache lock => need to find the session holding the lock, look for DML manipulating an object being accessed, if the session is trying to recompile PL/SQL, look for other sessions executing the code. undo segment extension => If excessive, tune undo. wait for a undo record => Usually only during recovery of large transactions, look at turning off parallel undo recovery.

enque wait events => Look at V$ENQUEUE_STAT

SQL*Net message from client
SQL*Net message from dblink
SQL*Net more data from client
SQL*Net message to client
SQL*Net break/reset to client

7. What are the init parameters related to performance/optimizer? optimizer_mode = choose optimizer_index_caching = 90 optimizer_index_cost_adj = 25 optimizer_max_permutations = 100 optimizer_use_sql_plan_baselines=true optimizer_capture_sql_plan_baselines=true optimizer_use_pending_statistics = true; optimizer_use_invisible_indexes=true _optimizer_connect_by_cost_based=false
_optimizer_compute_index_stats= true;

8. What are the values of optimizer_mode init parameters and their meaning? optimizer_mode = choose

9. What is the use of AWR, ADDM, ASH?
AWR : automatic workload repository
The AWR is used to collect performance statistics including:
•Wait events used to identify performance problems.
•Time model statistics indicating the amount of DB time associated with a process from the V$SESS_TIME_MODEL and V$SYS_TIME_MODEL views.
•Active Session History (ASH) statistics from the V$ACTIVE_SESSION_HISTORY view.
•Some system and session statistics from the V$SYSSTAT and V$SESSTAT views.
•Object usage statistics.
•Resource intensive SQL statements.
ADDM : automatic database diagnostic monitor analyzes data in the Automatic Workload Repository (AWR) to identify potential performance bottlenecks.and we use it for the following cases :
• CPU bottlenecks
• Undersized memory structures
• I/O capacity issues
• High load SQL statements
• RAC specific issues
• Database configuration issues
• Also provides recommendations on hardware changes, database configuration & schema changes.
Generate ADDM :

•Login to SQL
•@$ORACLE_HOME/rdbms/admin/addmrpt.sql
• enter system password when you asked for .
•Specify a begin_snap from the list and press Enter.
•Specify the end_snap from the list and press Enter.
• Report Name
ASH : Active Session History statistics from the in-memory performance monitoring tables also used to track session activity and simplify performance tuning.
ASH reports Give the following information :
•Top User Events (frequent wait events)
•Details to the wait events
•Top Queries
•Top Sessions
•Top Blocking Sessions
•Top DB Object.
•Activity Over Time Generate ASH reports : The Best way to do that using OEM. (Enterprise manager).

10. How to generate AWR report and what are the things you will check in the report?

11. How to generate ADDM report and what are the things you will check in the report?

12. How to generate ASH report and what are the things you will check in the report?

13. How to generate STATSPACK report and what are the things you will check in the report?

14. How to generate TKPROF report and what are the things you will check in the report?
The tkprof tool is a tuning tool used to determine cpu and execution times for SQL statements. Use it by first setting timed_statistics to true in the initialization file and then turning on tracing for either the entire database via the sql_trace parameter or for the session using the ALTER SESSION command. Once the trace file is generated you run the tkprof tool against the trace file and then look at the output from the tkprof tool. This can also be used to generate explain plan output.
-------------------------------------------------
Oracle Performance Tuning Interview Questions and Answers

Application user is complaining the database is slow. How would you find the performance issue of SQL queries?
High performance is common expectation for end user, in fact the database is never slow or fast in most of the case session connected to the database slow down when they receives unexpected hit. Thus to solve this issue you need to find those unexpected hit. To know exactly what the session is doing join your query v$session with v$session_wait.
SELECT NVL(s.username,'(oracle)') as username,s.sid,s.serial#,sw.event,sw.wait_time, sw.seconds_in_wait, sw.state FROM v$session_wait sw,v$session s
WHERE s.sid=sw.sid and s.username= '&username'ORDER BY sw.seconds_in_wait DESC;

1.Check the events that are waiting for something.
2. Try to find out the objects locks for that particular session.
3. Locking is not only the cause to effects the performance. Disk I/O contention is another case. When a session retrieves data from the database datafiles on disk to the buffer cache, it has to wait until the disk sends the data. The wait event shows up for the session as "db file sequential read" (for index scan) or "db file scattered read" (for full table scan).When you see the event, you know that the session is waiting for I/O from the disk to complete. To improve session performance, you have to reduce that waiting period. The exact step depends on specific situation, but the first technique “reducing the number of blocks retrieved by a SQL statement” almost always works. Reduce the number of blocks retrieved by the SQL statement. Examine the SQL statement to see if it is doing a full-table scan when it should be using an index, if it is using a wrong index, or if it can be rewritten to reduce the amount of data it retrieves.
4. Run SQL Tuning Advisor (@$ORACLE_HOME/rdbms/admin/sqltrpt.sql) by providing SQL_ID as the input for generating the findings and recommendations.
SQL Tuning Advisor seems to be doing logical optimization mainly by checking your SQL structure and statistics.
SQL Tuning Advisor suggests indexes that might be very useful.
SQL Tuning Advisor suggests query rewrites.
SQL Tuning Advisor suggests SQL profile.

More:
1.Run TOP command in Linux to check CPU usage.
2. Run VMSTAT, SAR, PRSTAT command to get more information on CPU, memory usage and possible blocking.
3. Enable the trace file before running your queries,then check the trace file using tkprof create output file.
According to explain plan check the elapsed time for each query,then tune them respectively.

What is the use of iostat/vmstat/netstat command in Linux?
Iostat – reports on terminal, disk and tape I/O activity.
Vmstat – reports on virtual memory statistics for processes, disk, tape and CPU activity.
Netstat – reports on the contents of network data structures.

If you are getting high “Busy Buffer waits”, how can you find the reason behind it?
Buffer busy wait means that the queries are waiting for the blocks to be read into the db cache. There could be the reason when the block may be busy in the cache and session is waiting for it. It could be undo/data block or segment header wait.
Run the below two query to find out the P1, P2 and P3 of a session causing buffer busy wait then after another query by putting the above P1, P2 and P3 values.
SQL> Select p1 "File #",p2 "Block #",p3 "Reason Code" from v$session_wait Where event = 'buffer busy waits';
SQL> Select owner, segment_name, segment_type from dba_extents
Where file_id = &P1 and &P2 between block_id and block_id + blocks -1;
What to Look for in AWR Report and STATSPACK Report?
Many DBAs already know how to use STATSPACK but are not always sure what to check regularly.
Remember to separate OLTP and Batch activity when you run STATSPACK, since they usually generate different types of waits. The SQL script “spauto.sql” can be used to run STATSPACK every hour on the hour. See the script in $ORACLE_HOME/rdbms/admin/spauto.sql for more information (note that JOB_QUEUE_PROCESSES must be set > 0). Since every system is different, this is only a general list of things you should regularly check in your STATSPACK output:
¦ Top 5 wait events (timed events)
¦ Load profile
¦ Instance efficiency hit ratios
¦ Wait events

¦ Latch waits
¦ Top SQL
¦ Instance activity
¦ File I/O and segment statistics
¦ Memory allocation
¦ Buffer waits What is the difference between DB file sequential read and DB File Scattered Read?
DB file sequential read is associated with index read where as DB File Scattered Read has to do with full table scan.
The DB file sequential read, reads block into contiguous memory and DB File scattered read gets from multiple block and scattered them into buffer cache.

Which factors are to be considered for creating index on Table? How to select column for index?
Creation of index on table depends on size of table, volume of data. If size of table is large and we need only few data for selecting or in report then we need to create index. There are some basic reason of selecting column for indexing like cardinality and frequent usage in where condition of select query. Business rule is also forcing to create index like primary key, because configuring primary key or unique key automatically create unique index.
It is important to note that creation of so many indexes would affect the performance of DML on table because in single transaction should need to perform on various index segments and table simultaneously.

Is creating index online possible?
YES. You can create and rebuild indexes online. This enables you to update base tables at the same time you are building or rebuilding indexes on that table. You can perform DML operations while the index building is taking place, but DDL operations are not allowed. Parallel execution is not supported when creating or rebuilding an index online.
CREATE INDEX emp_name ON emp (mgr, emp1, emp2, emp3) ONLINE;

How to recover password in oracle 10g?
You can query with the table user_history$. The password history is store in this table.

How can you track the password change for a user in oracle?
Oracle only tracks the date that the password will expire based on when it was latest changed. Thus listing the view DBA_USERS.EXPIRY_DATE and subtracting PASSWORD_LIFE_TIME you can determine when password was last changed. You can also check the last password change time directly from the PTIME column in USER$ table (on which DBA_USERS view is based). But If you have PASSWORD_REUSE_TIME and/or PASSWORD_REUSE_MAX set in a profile assigned to a user account then you can reference dictionary table USER_HISTORY$ for when the password was changed for this account.
SELECT user$.NAME, user$.PASSWORD, user$.ptime, user_history$.password_date
FROM SYS.user_history$, SYS.user$
WHERE user_history$.user# = user$.user#;

What is Secure External password Store (SEPS)?
Through the use of SEPS you can store password credentials for connecting to database by using a client side oracle wallet, this wallet stores signing credentials. This feature introduced since oracle 10g. Thus the application code, scheduled job, scripts no longer needed embedded username and passwords. This reduces risk because the passwords are no longer exposed and password management policies are more easily enforced without changing application code whenever username and password change.

Why we need CASCADE option with DROP USER command whenever dropping a user and why "DROP USER" commands fails when we don't use it?
If a user having any object then ‘YES’ in that case you are not able to drop that user without using CASCADE option. The DROP USER with CASCADE option command drops user along with its all associated objects. Remember it is a DDL command after the execution of this command rollback cannot be performed.

What is the difference between Redo, Rollback and Undo?
I find there is always some confusion when talking about Redo, Rollback and Undo. They all sound like pretty much the same thing or at least pretty close.
Redo: Every Oracle database has a set of (two or more) redo log files. The redo log records all changes made to data, including both uncommitted and committed changes. In addition to the online redo logs Oracle also stores archive redo logs. All redo logs are used in recovery situations.
Rollback: More specifically rollback segments. Rollback segments store the data as it was before changes were made. This is in contrast to the redo log which is a record of the insert/update/deletes.
Undo: Rollback segments. They both are really one in the same. Undo data is stored in the undo tablespace. Undo is helpful in building a read consistent view of data.

You have more than 3 instances running on the Linux server? How can you determine which shared memory and semaphores are associated with which instance?
Oradebug is undocumented oracle supplied utility by oracle. The oradebug help command list the command available with oracle.
SQL>oradebug setmypid
SQL>oradebug ipc
SQL>oradebug tracfile_name

Why drop table is not going into Recycle bin?
If you are using SYS user to drop any table then user’s object will not go to the recyclebin as there is no recyclebin for SYSTEM tablespace, even we have already SET recycle bin parameter TRUE.
Select * from v$parameter where name = 'recyclebin';
Show parameter recyclebin;

Temp Tablespace is 100% FULL and there is no space available to add datafiles to increase temp tablespace. What can you do in that case to free up TEMP tablespace?
Try to close some of the idle sessions connected to the database will help you to free some TEMP space. Otherwise you can also use ‘Alter Tablespace PCTINCREASE 1’ followed by ‘Alter Tablespace PCTINCREASE 0’

When a Tablespace reaches 90%, what action you will take? How you decide whether to go for Resize or Add datafile?

What is the max possible size of a SMALL and BIG datafiles?

SUPPOSE A QUERY IS RUNNING SLOW OR HUNG STATE, What will you do?

SUPPOSE DATAABSE IS RUNNING SLOW, What will you do?

As a DBA what Pro active steps do you take for a Highly utilized Undo?

AWR Vs. ASH?

AWR Contents?How to interpret AWR?

Wait Events?

Difference between DB File Sequential Read and DB file Scattered Reads?

how to cache a table or pin a table?

What is explain plan?

What is Database Replay?

What is Fragmentaion?

What are MATERIALIZED VIEWS?

What are Trace files?

What is ORA-600?

What is OLTP AND DATAWAREHOUSING?

How to change character set of database?

What are unused indexes?How to reuse unused indexes?
What is Row Chaning and Row Migration?
Row Migration:
A row migrates when an update to that row would cause it to not fit on the block anymore (with all of the other data that exists there currently). A migration means that the entire row will move and we just leave behind the «forwarding address». So, the original block just has the rowid of the new block and the entire row is moved.

Row Chaining:
A row is too large to fit into a single database block. For example, if you use a 4KB blocksize for your database, and you need to insert a row of 8KB into it, Oracle will use 3 blocks and store the row in pieces.
Some conditions that will cause row chaining are: Tables whose rowsize exceeds the blocksize. Tables with LONG and LONG RAW columns are prone to having chained rows. Tables with more then 255 columns will have chained rows as Oracle break wide tables up into pieces.
So, instead of just having a forwarding address on one block and the data on another we have data on two or more blocks.

How to find out background processes ?
SQL> select SID,PROGRAM from v$session where TYPE='BACKGROUND';
SQL> select name,description from V$bgprocess;

How to findout background processes from OS:
$ ps -ef|grep ora_|grep SID
To Find and Delete bigger size and older files in Linux
--To find out files size more than 5MB find . -size +5000 -exec ls -ltr {} \;
-- To **Remove** files size more than 5MB find . -size +5000k -exec rm -rf {} \;
--To find out files older than 30days find . -mtime +30 -exec ls -ltr {} \;
--To find **Remove** files older than 30days
-------------------------------------------------
find . -mtime +30 -exec rm -rf {} \;

Oracle Export/Import (exp/imp)- Data Pump (expdp/imp) Interview Questions and Answers

1. What is use of CONSISTENT option in exp?
Cross-table consistency. Implements SET TRANSACTION READ ONLY. Default value N.

2. What is use of DIRECT=Y option in exp?
Setting direct=yes, to extract data by reading the data directly, bypasses the SGA, bypassing the SQL command-processing layer (evaluating buffer), so it should be faster. Default value N.

3. What is use of COMPRESS option in exp?
Imports into one extent. Specifies how export will manage the initial extent for the table data. This parameter is helpful during database re-organization. Export the objects (especially tables and indexes) with COMPRESS=Y. If table was spawning 20 Extents of 1M each (which is not desirable, taking into account performance), if you export the table with COMPRESS=Y, the DDL generated will have initial of 20M. Later on when importing the extents will be coalesced. Sometime it is found desirable to export with COMPRESS=N, in situations where you do not have contiguous space on disk (tablespace), and do not want imports to fail.

4. How to improve exp performance?
1. Set the BUFFER parameter to a high value. Default is 256KB.
2. Stop unnecessary applications to free the resources.
3. If you are running multiple sessions, make sure they write to different disks.
4. Do not export to NFS (Network File Share). Exporting to disk is faster.
5. Set the RECORDLENGTH parameter to a high value.
6. Use DIRECT=yes (direct mode export).

5. How to improve imp performance?
1. Place the file to be imported in separate disk from datafiles.
2. Increase the DB_CACHE_SIZE.
3. Set LOG_BUFFER to big size.
4. Stop redolog archiving, if possible.
5. Use COMMIT=n, if possible.
6. Set the BUFFER parameter to a high value. Default is 256KB.
7. It's advisable to drop indexes before importing to speed up the import process or set INDEXES=N and building indexes later on after the import. Indexes can easily be recreated after the data was successfully imported.
8. Use STATISTICS=NONE
9. Disable the INSERT triggers, as they fire during import.
10. Set Parameter COMMIT_WRITE=NOWAIT(in Oracle 10g) or COMMIT_WAIT=NOWAIT (in Oracle 11g) during import.

6. What is use of INDEXFILE option in imp?
Will write DDLs of the objects in the dumpfile into the specified file.

7. What is use of IGNORE option in imp?
Will ignore the errors during import and will continue the import.

8. What are the differences between expdp and exp (Data Pump or normal exp/imp)?
Data Pump is server centric (files will be at server).
Data Pump has APIs, from procedures we can run Data Pump jobs.
In Data Pump, we can stop and restart the jobs.
Data Pump will do parallel execution.
Tapes & pipes are not supported in Data Pump.
Data Pump consumes more undo tablespace.
Data Pump import will create the user, if user doesn’t exist.

9. Why expdp is faster than exp (or) why Data Pump is faster than conventional export/import?
Data Pump is block mode, exp is byte mode.
Data Pump will do parallel execution.
Data Pump uses direct path API.

10. How to improve expdp performance?
Using parallel option which increases worker threads. This should be set based on the number of cpus.

11. How to improve impdp performance?
Using parallel option which increases worker threads. This should be set based on the number of cpus.

12. In Data Pump, where the jobs info will be stored (or) if you restart a job in Data Pump, how it will know from where to resume?
Whenever Data Pump export or import is running, Oracle will create a table with the JOB_NAME and will be deleted once the job is done. From this table, Oracle will find out how much job has completed and from where to continue etc.
Default export job name will be SYS_EXPORT_XXXX_01, where XXXX can be FULL or SCHEMA or TABLE.
Default import job name will be SYS_IMPORT_XXXX_01, where XXXX can be FULL or SCHEMA or TABLE.

13. What is the order of importing objects in impdp? Tablespaces Users Roles Database links Sequences Directories Synonyms Types Tables/Partitions Views Comments Packages/Procedures/Functions Materialized views

14. How to import only metadata?
CONTENT= METADATA_ONLY

15. How to import into different user/tablespace/datafile/table?
REMAP_SCHEMA
REMAP_TABLESPACE
REMAP_DATAFILE
REMAP_TABLE
REMAP_DATA

16. How to export/import without using external directory?

17. Using Data Pump, how to export in higher version (11g) and import into lower version (10g), can we import to 9i?
Export/Import between different releases of Oracle
Oracle Data Pump was first released in Oracle 10g (expdp and impdp). Priot to Data Pump, Oracle used the "exp" and "imp" utilities.
In your case, both the export (expdp) and import (impdp) are with Data Pump and you can use the version [parameter to export from a later release of Oracle an import that dump file into an earlier release of Oracle.
You can import your 11g expdp dump file into Oracle 10g if you make sure you use "VERSION=10.2" parameter during export.
Here is a working example of using the expdp version parameter to make a dump file acceptable to an earlier release of Oracle:
Export using the expdp version parameter:
C:\Users\Steve>expdp hr/hr TABLES=hr.employees2 VERSION=10.2 DIRECTORY=data_pump_dir DUMPFILE=emp2.dmp LOGFILE=emp2.log

Export: Release 11.2.0.1.0 - Production on Tue Sep 7 09:10:51 2010

Copyright (c) 1982, 2009, Oracle and/or its affiliates. All rights reserved.

Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production

With the Partitioning, OLAP, Data Mining and Real Application Testing options

Starting "HR"."SYS_EXPORT_TABLE_01": hr/******** TABLES=hr.employees2 VERSION=10.2 DIRECTORY=data_pump_dir DUMPFILE=emp2.dmp LOGFILE=emp2.log

Estimate in progress using BLOCKS method...
Processing object type TABLE_EXPORT/TABLE/TABLE_DATA
Total estimation using BLOCKS method: 64 KB

Processing object type TABLE_EXPORT/TABLE/TABLE

. . exported "HR"."EMPLOYEES2" 16.12 KB 107 rows

Master table "HR"."SYS_EXPORT_TABLE_01" successfully loaded/unloaded
******************************************************************************

Dump file set for HR.SYS_EXPORT_TABLE_01 is: C:\APP\ORACLE\ADMIN\ORCL\DPDUMP\EMP2.DMP

Job "HR"."SYS_EXPORT_TABLE_01" successfully completed at 09:11:01
Import into earlier release of Oracle:
Here we copied the dmp file from the 11g directory to the 10g dump file location and execute expdp on the 10g instance:
DIRECTORY_NAME DIRECTORY_PATH
------------------------------ ----------------------------------------
DATA_PUMP_DIR C:\oraclexe\app\oracle\admin\XE\dpdump\
ORACLECLRDIR C:\oraclexe\app\oracle\product\10.2.0\se rver\bin\clr

SQL> grant read, write on directory data_pump_dir to hr;

Grant succeeded.

SQL> exit

Disconnected from Oracle Database 10g Express Edition Release 10.2.0.1.0 - Production

C:\Users\Steve>impdp hr/hr TABLES=hr.employees2 DIRECTORY=data_pump_dir DUMPFILE=emp2.dmp LOGFILE=emp2_imp.log

Import: Release 10.2.0.1.0 - Production on Tuesday, 07 September, 2010 9:25:53

Copyright (c) 2003, 2005, Oracle. All rights reserved.

Connected to: Oracle Database 10g Express Edition Release 10.2.0.1.0 - Production

Master table "HR"."SYS_IMPORT_TABLE_01" successfully loaded/unloaded

Starting "HR"."SYS_IMPORT_TABLE_01": hr/******** TABLES=hr.employees2 DIRECTORY=data_pump_dir DUMPFILE=emp2.dmp LOGFILE=emp2_imp.log

Processing object type TABLE_EXPORT/TABLE/TABLE
Processing object type TABLE_EXPORT/TABLE/TABLE_DATA

. . imported "HR"."EMPLOYEES2" 16.12 KB 107 rows

Job "HR"."SYS_IMPORT_TABLE_01" successfully completed at 09:26:05

C:\Users\Steve>sqlplus hr/hr

SQL*Plus: Release 10.2.0.1.0 - Production on Tue Sep 7 09:26:37 2010

Copyright (c) 1982, 2005, Oracle. All rights reserved.

Connected to:

Oracle Database 10g Express Edition Release 10.2.0.1.0 - Production

SQL> select count(*) from employees2;

COUNT(*)
----------
107

18. Using normal exp/imp, how to export in higher version (11g) and import into lower version (10g/9i)?
Using exp with impdp to import into an earlier release
In general, there was a major change between the older export utility (exp) and the data pump export (expdp), and Oracle notes that exports from newer releases cannot be imported into earlier releases:
"The version of the Import utility cannot be earlier than the version of the Export utility used to create the dump file. "
* The Import utility and the database to which data is being imported (the target database) must be the same version.

* The version of the Export utility must be equal to the earliest version of the source or target database.
For example, to create an export file for an import into a later release database, use a version of the Export utility that is equal to the source database. Conversely, to create an export file for an import into an earlier release database, use a version of the Export utility that is equal to the version of the target database.

Original Export and Import do not support all Oracle Database 10g features. . . .

However, you should still use the original Export and Import utilities in the following situations:

* You want to import files that were created using the original Export utility (exp).

* You want to export files that will be imported using the original Import utility (imp). An example of this would be if you wanted to export data from Oracle Database 10g and then import it into an earlier database release. "

An unsupported solution to importing into an older database
It's not supported, but you might be able to use the pre-data pump export program (exp, NOT expdp) and use it to export data. Note that you may need to run the old $ORACLE_HOME/rebms/admin/catexp.sql from 9i on the 10g dictionary.

Then you might be able to import:
1 - copy the executable to the Oracle_home/bin and re-name as exp9i.exe

or possibly:

2 - Invoke the exp utility, pointing it to the 10g database with a database link.

19. How to do transport tablespaces (and across platforms) using exp/imp or expdp/impdp?
Transport Tablespaces
1. Using exp/imp
2. Using expdp/impdp
3. Using expdp/impdp with database link.
4. Cross platform transport tablespace. http://smahamed.blogspot.in/2010/11/transport-tablespaces.html UNIX Interview Questions and Answers for Oracle DBAs

1. How do you list the files in an UNIX directory while also showing hidden files? ls -ltra 2. How do you execute a UNIX command in the background?
Use the "&" at the end of command 3. What UNIX command will control the default file permissions when files are created? Umask 4. Explain the read, write, and execute permissions on a UNIX directory.
Read allows you to see and list the directory contents. Write allows you to create, edit and delete files and subdirectories in the directory. Execute gives you the previous read/write permissions plus allows you to change into the directory and execute programs or shells from the directory.
5. The difference between a soft link and a hard link?
A symbolic (soft) linked file and the targeted file can be located on the same or different file system while for a hard link they must be located on the same file system.
6. Give the command to display space usage on the UNIX file system. df -lk
7. Explain iostat, vmstat and netstat.
Iostat reports on terminal, disk and tape I/O activity.
Vmstat reports on virtual memory statistics for processes, disk, tape and CPU activity.
Netstat reports on the contents of network data structures.
8. How would you change all occurrences of a value using VI?
Use:%s/<old>/<new>/g
9. Give two UNIX kernel parameters that effect an Oracle install
SHMMAX & SHMMNI
10. Briefly, how do you install Oracle software on UNIX.
Basically, set up disks, kernel parameters, create oracle user and dba group, and run runinstaller.
11. How do you create a decision tree in a shell script?
Oepending on shell, usually a case-esac or an if-endif or fi structure
12. What is a pipe and give an example?
A pipe is two or more commands separated by pipe char '|'. That tells the shell to arrange for the output of the preceding command to be passed as input to the following command.
Example : ls -l | pr
The output for a command ls is the standard input of pr. When a sequence of commands are combined using pipe, then it is called pipeline.
13. What is the difference between > and >> redirection operators?
> is the output redirection operator when used it overwrites while >> operator appends into the file.
14. What is the difference between process and thread.
Creation of new process requires new resources and Address space whereas the thread can be created in the same address space of the process which not only saves space and resources but are also easy to create and delete, and many threads can exists in a process.
15. What is the difference between a shell variable that is exported and the one that is not exported? export LANG=C will make the variable LANG the global variable, put it into the global environment. all other processes can use it.
LANG=C will change the value only in the current script.
16. How will you list only the empty lines in a file (using grep) grep "^$" filename.txt
17. What is Semaphore?
A data object that represents the right to use a limited resource, used for synchronization and communication between asynchronous processes.
18. How do you execute a UNIX command in the background?
You can use & at the end of command or use nohup command
19. How do you check active shared memory segments? ipcs -a
20. How do you check Paging/Swapping in Unix?
You can check Paging/Swapping using below commands vmstat s prstat s swap l sar p
21. How do you check number of CPU installed on Unix server? psrinfot v

22. What’s the difference between soft link and hard link? A symbolic (soft) linked file and the targeted file can be located on the same or different file system while for a hard link they must be located on the same file system, because they share same inode number and an inode table is unique to a file system, both must be on the same file system.

23. How you will read a file from shell script? while read line do echo $line done < file_name

24. What’s the use of umask?
Will decide the default permissions for files.

25. What is crontab and what are the arguments? The entries have the following elements: field allowed values
----- -------------- minute 0-59 hour 0-23 day of month 1-31 month 1-12 day of week 0-7 (both 0 and 7 are Sunday) user Valid OS user command Valid command or script

? ? ? ? ? command
| | | | |_________day of the week (0-6, 0=Sunday)
| | | |___________month (1-12)
| | |_____________day of the month (1-31)
| |_______________hour (0-23)
|_________________minute (0-59)

26. How to find operating system (OS) version? uname –a

27. How to find out the run level of the user? uname –r

28. How to delete 7 days old trace files? find ./trace –name *.trc –mtime +7 –exec rm {} \;

29. How to get 10th line of a file (by using grep)?

30. (In Solaris) how to find out whether it’s 32bit or 64bit?

31. What is paging?

32. What is top command? top is a operating system command, it will display top processes which are taking high cpu and memory.

33. How to find out the status of last command executed? $?

34. How to find out number of arguments passed to a shell script? $#

35. What is the default value of umask? 022

36. How to add user in Solaris/Linux?
Ans:
useradd command