Sep 18, 2009

Block Change Tracking in Oracle



Oracle Block change Tracking is introduced in 10g.Its used to track the changed blocks of a database to a tracking file and used for better performance of incremental backups. If block change tracking is enabled for a database RMAN uses block change tracking file to identify changed blocks for incremental backups instead full data file scans during the backup.

By default, Block change tracking is disabled for a database. You can Enable or disable the change tracking when the database is open or mounted.

You can check the status of block change tracking using the below query.

SQL> SELECT FILE,STATUS,BYTES FROM V$BLOCK_CHANGE_TRACKING;

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

Create change tracking file in a specified location.
SQL> ALTER DATABASE ENABLE BLOCK CHANGE TRACKING USING FILE /oracle/fra/bct.log';

Create change tracking file in ASM disk group.
SQL>ALTER DATABASE ENABLE BLOCK CHANGE TRACKING USING FILE '+DGROUP_FR1';

Disable Block Change Tracking:
Use the below command to disable block change tracking
SQL> ALTER DATABASE DISABLE BLOCK CHANGE TRACKING;
Note: When disabled oracle will automatically delete the tracking file from physical  
         location.

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

Change location of Tracking file:
you must disable block change tracking before you move it to new location.

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

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

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