Oracle 10g - RMAN Block change tracking

There are performance issues associated with incremental backups where most of the times we have issues with the CPU/IO being consumed more. In Oracle 10g it is possible to track changed blocks using a change tracking file.

Prior to introduction of Oracle 10g block change tracking (BCT), RMAN had to scan the whole datafile to and filter out the blocks that were not changed since base incremental backup and overhead or incremental backup was as high as full backup. Oracle 10g new feature, block change tracking, minimizes number of blocks RMAN needs to read to a strict minimum. With block change tracking enabled RMAN accesses on disk only blocks that were changed since the latest base incremental backup.

Enabling change tracking does produce a small overhead, but it greatly improves the performance of incremental backups.

The current change tracking status can be displayed using the following query:
SELECT status FROM v$block_change_tracking;

Change tracking is enabled using the ALTER DATABASE command:
ALTER DATABASE ENABLE BLOCK CHANGE TRACKING USING FILE '/ts1/oradata/block_change_track.dbf';

The tracking file is created with a minumum size of 10M and grows in 10M increments. It's size is typically 1/30,000 the size of the datablocks to be tracked.

Change tracking can be disabled using the following command:
ALTER DATABASE DISABLE BLOCK CHANGE TRACKING;

Renaming or moving a tracking file can be accomplished in the normal way using the ALTER DATABASE RENAME FILE command. If the instance cannot be restarted you can simply disable and re-enable change tracking to create a new file. This method does result in the loss of any current change information.

Background Process – Change Tracking Writer (CTWR). This process takes care of logging information about changed blocks in block change tracking file.