Tuesday, September 1, 2009

Block Change Tracking in Oracle 10g

Oracle Block change Tracking improves the incremental Backup performance and is used to record changed blocks in each datafile in a change tracking file. If change Tracking is enabled, RMAN uses block change tracking file to identify changed blocks for incremental backups and avoids full datafile scans during the backup.

Block change tracking feature introduce in Oracle 10g R1. By default, the Block change tracking file is created as Oracle managed file in DB_CREATE_FILE_DEST.

By default, Oracle will not record block change information. You can Enable or disable the change tracking when the database is open or mounted.

Enable and Disable Block Change Tracking:
Run the below command to enable block change tracking
SQL>ALTER DATABASE ENABLE BLOCK CHANGE TRACKING;

Run the below command to create change tracking file in a specified location.
SQL> ALTER DATABASE ENABLE BLOCK CHANGE TRACKING
USING FILE '/oradata/block_change_track.ora' REUSE;

Run the below command to disable block change tracking
SQL> ALTER DATABASE DISABLE BLOCK CHANGE TRACKING;

Run the below Query to monitor the status of block change tracking
SQL> SELECT FILE,STATUS,BYTES FROM V$BLOCK_CHANGE_TRACKING;

Moving Block Change tracking file without Database shutdown:
If your database is 24x7 critical production and you cannot shut down, then follow the below steps. Please note that you must disable change tracking and you will lose the old contents of the change tracking file, if you choose this method.

Step1: Disable the change tracking
SQL> ALTER DATABASE DISABLE BLOCK CHANGE TRACKING;

Step2: Re-enable it at the new location
SQL> ALTER DATABASE ENABLE BLOCK CHANGE TRACKING USING FILE 'new_location';

Moving Block Change tracking file with Database shutdown:
Step1: Determine the change tracking file:
SQL> SELECT filename FROM V$BLOCK_CHANGE_TRACKING;

Step2: shutdown and move or copy the tracking file.
SQL> SHUTDOWN IMMEDIATE
$ cp ‘/old_lockation/block_change_tracking.ora’ ‘/new_location/ block_change_tracking.ora’

Step3: Mount the database and rename change tracking file to new location.
SQL> STARTUP MOUNT;
SQL> ALTER DATABASE RENAME FILE ‘old_location’ TO ‘new_location’;

Step4: Open the database
SQL> ALTER DATABASE OPEN;

Block change tracking in RAC (Real Applications Clusters) environment, the file must be located on shared storage so that the file is accessible for all the nodes.

Regards,
Satishbabu Gunukula
http://www.oracleracexpert.com/

2 comments:

  1. RMAN's change tracking feature for incremental backups improves incremental backup performance by recording changed blocks in each datafile in a change tracking file. If change tracking is enabled, RMAN uses the change tracking file to identify changed blocks for incremental backup, thus avoiding the need to scan every block in the datafile.

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