Oracle Data Guard Interview Questions & Answers


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

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.

38 comments:

  1. Very Useful...
    If I did see this befor my last interview..I would have cleared it...:-(

    ReplyDelete
  2. Ajaz: Very good and helpful content.

    ReplyDelete
  3. Mohammed: Answers explained very well.

    ReplyDelete
  4. This comment has been removed by the author.

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  5. its really very very useful ....thank you verymuch

    ReplyDelete
  6. Hi, minor typo error. Should be FAL_CLIENT and FAL_SERVER rather than FAT_xxxxx
    BTW, thanks for this post

    ReplyDelete
    Replies
    1. Joseph you are right. Thanks to solve my confusion regarding FAT and FAL.

      Delete
  7. Very nice content, it is helpful for me....

    ReplyDelete
  8. very good, it's helpful for us..

    ReplyDelete
  9. Hi ,

    Ver

    If i add a datafile on primary database can it will be added on standby if yes how ?

    ReplyDelete
    Replies
    1. Hi,
      For the above question:
      if you set the standby_file_management parameter in the standby database side to AUTO then datafile will be added automatically.
      SQL> show parameter standby_file_management

      NAME TYPE VALUE
      ------------------------------------ -------------------- ------------------------------
      standby_file_management string AUTO
      SQL>

      Delete
  10. Typo error:
    ALTER DATABASE SET STANDBY DATABASE TO MAXIMIZE [PROTECTION|PERFORMANCE|AVAILABILITY];
    instead of
    ALTER DATABASE SET STANDBY DATABASE TO MAXIMUM [PROTECTION|PERFORMANCE|AVAILABILITY];

    ReplyDelete
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  12. very good explanation...appreciate your effort.

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  13. Excellent article. The descriptions are to the point. You need to add more questions and explanations about Data Guard.

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