DataGuard Interview Questions

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.

What are the different services available in Oracle Data Guard?

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

  • Redo Transport Services.
  • Log Apply Services.
  • Role -Transitions.

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

Below are the protection modes available in DG

  1. Maximum Protection
  2. Maximum Availability
  3. 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.

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


How to change protection mode in Oracle Data Guard setup?


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

  1. High Availability.
  2. Load balancing (Backup and Reporting).
  3. Data Protection.
  4. Disaster Recovery.

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.

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

The services required on the primary database are:

  1. 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.
  2. Archiver Process (ARCn): One or more archiver processes make copies of online redo logs either locally or remotely for standby databases.
  3. 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.
  4. 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:

  1. 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.
  2. Remote File Server (RFS): Receives archived and/or standby redo logs from the primary database.
  3. Archiver (ARCn) Processes: Archives the standby redo logs applied by the managed recovery process (MRP).
  4. Managed Recovery Process (MRP): pplies archive redo log information to the standby database.

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:

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

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

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

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.

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.

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:


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.

Online Oracle Data Guard Training

Oracle Data Guard Interview Questions

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.

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

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

ADG – in READ ONLY state, MRP will apply the 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.

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.

What are the parameters we’ve to set in primary/standby for Data Guard?












What is the use of fal_server & fal_client, is it mandatory to set these?


specifies the FAL (fetch archive log) server for a standby database. The value 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.


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 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).

How to find out backlog 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);

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;

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.

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.

What is active data guard? Does it needs additional licensing?

Active dataguard means, the standby database is open with read only mode, when redo logs are                 getting applied in real time.

Below are the benefit of using active dataguard.

  • Reporting queries can be offloaded to standby database.
  • Physical block corruptions are repaired automatically either at primary or physical standby database.
  • RMAN backups can be initiated from standby , instead of primary which will reduce cpu load from primary.

What is active dataguard duplicate?

Starting from 11g we can duplicate database by two way 1) Active DB duplicate 2) Backup-based                  duplicate.

Active DB duplicate copies the live TARGET DB over the network to the AUXILLARY destination and      then create the duplicate database. In an active duplication process, target database online image              copies and archived redo log files were copied through the auxiliary instance service name. So there is      no need of target db backup.