Making Backups with RMAN - RMAN Recipes for Oracle Database 12c - page 193

Reducing Incremental Backup Time
Problem
You want to reduce the time it takes to perform incremental backups.

Solution
Implement RMAN's block change tracking feature to reduce the time it takes to make an RMAN incremental backup.
By default, the block change tracking feature is disabled. Use the following command to create a change tracking file
in the specified location (if you leave out the location, RMAN creates the block change tracking file in the location
specified by the db_create_file_dest initialization parameter).

First, make sure the db_create_file_dest parameter is set. If it isn't, set it using the alter
system command, as shown in this example:

1.

SQL> alter system set
db_create_file_dest='/u01/app/oracle/dfiles'
scope= both;

Enable block change tracking by using the following alter database statement: 2.

RMAN> alter database enable block change tracking using file
'/u01/app/oracle/backup/change_track.f';

Statement processed

RMAN>
The name of the change tracking file is change_track.txt in our example.
You can disable block change tracking by using the following command:

RMAN> alter database disable block change tracking;

Statement processed

RMAN>

The change tracking file is automatically deleted when you execute the previous command.

How It Works
RMAN uses a binary file referred to as the block change tracking file to record the changed blocks in each data file in a
database. When you perform an incremental backup, RMAN refers to this change tracking file instead of scanning all
the data blocks in all the data files in the database, thus making the incremental backups finish faster. You can use the
alter database statement to change the name of the change tracking file.
The V$BLOCK_CHANGE_TRACKING view shows whether change tracking is enabled as well as other things
such as the change tracking file name.