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Thread: Enable block change tracking in Oracle for RMAN backups

  1. #1
    Expert Oracle Administrator
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    Enable block change tracking in Oracle for RMAN backups

    Enable block change tracking(Starting from 10g)
    ============================
    Note: Once enabled; this new 10g feature records the modified since last backup and stores the log of it in a block change tracking file.
    During backups RMAN uses the log file to identify the specific blocks that must be backed up. This improves RMAN's performance as it does not have to scan whole datafiles to detect changed blocks.Logging of changed blocks is performed by the CTRW process which is also responsible for writing data to the block change tracking file.
    Example :
    1. conn / as sysdba

    2. SELECT filename, status, bytes FROM v$block_change_tracking;
    -->Enable block change tracking
    3. ALTER DATABASE ENABLE BLOCK CHANGE TRACKING
    USING FILE 'c:\oracle\product lash_recovery_area\ORABASE\bctf01.log';

    4.
    SELECT filename, status, bytes FROM v$block_change_tracking;
    Regards,
    -Amit

  2. #2
    Oracle DBA
    Join Date
    Oct 2011
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    good one!!!

  3. #3
    Note :-- For Interview purpose Question.
    Qu:-- Do you know about Block change tracking in RMAN Utility and how it works in incremental backup ?.

    Ans:-- By default,this feature is disabled.This is the new feature of Oracle 10g.

    Block change tracking in RMAN:--

    Starting with Oracle 10g RMAN can take incremental backups without having to read the entire datafiles in order to find out which blocks have changed since the last backup.
    This new feature is called FAST INCREMENTAL BACKUP.
    The new technology used for this feature is called BLOCK CHANGE TRACKING.

    Fast Incremental Backups

    • RMAN reads change tracking file to find out which data blocks to read and copy during an incremental backup process, to avoid needing to read entire datafiles during incremental backups.

    • A new background process, the change tracking writer (CTWR), is in charge of writing the block change information to the change tracking file.

    Change Tracking File Features

    • The change tracking file contains the physical location of all database changes.

    • The minimum size is 10MB. Oracle creates the file automatically and allocates additional space in 10MB increments.

    • The file’s size depends on your database size, number of instances in an RAC, and the number of old backups the file maintains.

    • V$BLOCK_CHANGE_TRACKING shows the name, size, and status of your change tracking file.

    Enabling Block Change Tracking

    ALTER DATABASE
    ENABLE BLOCK CHANGE TRACKING
    USING FILE
    'C:\ORACLE\RECOVERY_AREA\CHANGETRACK.LOG'

    To relocate the file, while the databse is in mount mode:--

    ALTER DATABASE RENAME FILE
    'C:\ORACLE\RECOVERY_AREA\CHANGETRACK.LOG'
    TO 'C:\ORACLE\NEWCHANGE.LOG'

    To disable the block change tracking--:

    ALTER DATABASE DISABLE BLOCK CHANGE TRACKING;

    OR

    Note: Once enabled; this new 10g feature records the modified since last backup and stores the log of it in a block change tracking file. During backups RMAN uses the log file to identify the specific blocks that must be backed up. This improves RMAN's performance as it does not have to scan whole datafiles to detect changed blocks.

    Logging of changed blocks is performed by the CTRW process which is also responsible for writing data to the block change tracking file.
    Last edited by vineettyagi; 02-03-2012 at 02:15 PM.

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