Enabling Block Change Tracking

10G's Change Tracking feature improves the performance of incremental backups by recording datafile block changes in a change tracking file. Without Change Tracking, RMAN incremental backups are required to scan every block in the datafile to identify the blocks that have changed since the last database backup. Activating Change Tracking allows RMAN to read the change tracking file to identify the changed blocks. So, RMAN incremental backups should run much faster because they are no longer required to read each and every block in the datafile.

To increase performance on incremental database backups, enable block change tracking using the following command:

alter database enable block change tracking using file file_name;

If the db_create_file_dest parameter is set in the spfile or init.ora file of the database, the following command can be used:

alter database enable block change tracking;

Once you enable block change tracking, incremental database backup will use block change tracking.

The size of the change tracking file depends on the size of the database and not the frequency of updates. Oracle states that the size of the block tracking file is 1/30,000 the size of all the database data blocks being tracked by Change Tracking. Oracle also states that the file is created in 10 MB increments. For databases up to and including one terabyte, the size of the change tracking file will be 10MEGs, 2 terabyte databases will require 20MEGs and so on.