DATA GUARD INTERVIEW QUESTIONS & ANSWERS.

1.1. What are the advantages in using Oracle Data Guard?

1.  Following are the different benefits in using Oracle Data Guard feature in your environment.
2.   High Availability.
3.  Data Protection.
4.  Off-loading Backup operation to standby database.
5.  Automatic Gap detection and Resolution in standby database.
6.  Automatic Role Transition using Data Guard Broker.

22.  What are the different services available in Oracle Data Guard?

                Following are the different Services available in Oracle Data Guard of Oracle database.

ü  Redo Transport Services.

ü  Log Apply Services.

ü  Role -Transitions.

33. What are the different Protection modes available in Oracle Data Guard?

Below are the protection modes available in DG

ü  Maximum Protection

ü  Maximum Availability

ü  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.

4 4. How to check what protection mode of primary database in your Oracle Data Guard?

ü  SELECT PROTECTION_MODE FROM V$DATABASE;

5  5. How to change protection mode in Oracle Data Guard setup?

ALTER DATABASE SET STANDBY DATABASE TO MAXIMUM [PROTECTION|PERFORMANCE|AVAILABILITY];

6.6.  What are the advantages of using Physical standby database in Oracle Data Guard?

ü  High Availability.

ü  Load balancing (Backup and Reporting).

ü  Data Protection.

ü  Disaster Recovery.

7 7. What is the usage of DB_FILE_NAME_CONVERT parameter in Oracle Data Guard setup?

DB_FILE_NAME_CONVERT This parameter is used when you are using different directory structure in standby database compare to primary database data files location & also when we duplicating database this parameter can be used to generate files in a different location.

1 8.  What are the services required on the primary and standby data-base?

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.

Log network server (LNS): LNS is used on the primary to initiate a connection with the standby database.

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.

2  9.  What is RTS (Redo Transport Services) in Data-guard?

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:

ü  Transmit redo data from the primary system to the standby systems in the configuration.

ü  Manage the process of resolving any gaps in the archived redo log files due to a network failure.

ü  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.

ü  Control the automated transfer of redo data from a database destination to one or more destinations. Redo transport services also manage the process of resolving any gaps in the archived redo log files due to a network failure.

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

ü  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.

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

ü  Example: For 60min Delay:

ü  ALTER SYSTEM SET LOG_ARCHIVE_DEST_2=’SERVICE=stdby_srvc DELAY=60′;

ü  The DELAY attribute is expressed in minutes.

ü  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.

4.11.   How many standby databases we can create (in 10g/11g)?

ü  Till Oracle 10g, 9 standby databases are supported.

ü  From Oracle 11g R2, we can create 30 standby databases.

5.12. What are differences between physical, logical, snapshot standby and ADG (or) what are different types of standby databases?

ü  Physical standby – in MOUNT STATE, MRP proves will apply the archives

ü  ADG – in READ ONLY state, MRP will apply the archives

ü  Logical standby – in READ ONLY state, LSP will run

ü  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.