RMAN : Improving Incremental Backup Performance: Change Tracking

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.

After enabling change tracking, the first level 0 incremental backup still has to scan the entire datafile, as the change tracking file does not yet reflect the status of the blocks. Subsequent incremental backup that use this level 0 as parent will take advantage of the change tracking file.

Using change tracking in no way changes the commands used to perform incremental backups, and the change tracking files themselves generally require little maintenance after initial configuration.

Change tracking is disabled by default, because it does introduce some minimal performance overhead on your database during normal operations. However, the benefits of avoiding full datafile scans during backup are considerable, especially if only a small percentage of data blocks are changed between backups. If your backup strategy involves incremental backups, then you should enable change tracking.

One block change tracking file is created for the whole database. By default, the block change tracking file is created as an Oracle managed file in DB_CREATE_FILE_DEST. You can also specify the name of the block change tracking file, placing it in any location you choose.

How to enable Change Tracking:

SQL> ALTER DATABASE ENABLE BLOCK CHANGE TRACKING
USING FILE '/mydir/rman_change_track.f' REUSE;

You can view the status,filename,filesize
of Change Tracking in V$BLOCK_CHANGE_TRACKING view