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Brief of Incremental Backup

RMAN incremental backup option backs up blocks that have changed since the last incremental backup at the same level or below. For instance, a full backup (level_0) is taken on day 1 and two incrementals of level_1 are taken on days 2 and 3. The latter two merely back up the changed blocks between days 1 and 2 and days 2 and 3, not across the entire backup time. This strategy reduces backup size, requiring less space,
and narrows the backup window, reducing the amount of data moving across the network

In Oracle 9i and below, while doing incremental backup RMAN scans all the data blocks to identify changed
block for backup. This process puts so much stress on the system that doing incrementals becomes impractical.

Oracle Database 10g RMAN implements incremental backups in a manner that disposes of that objection. It uses a file, analogous to journals in filesystems, to track the blocks that have changed since the last backup. RMAN reads this file to determine which blocks are to be backed up.

You can enable this tracking mechanism by issuing the following command:

 SQL> alter database enable block change tracking using file ‘/usr2/oracle/backup/rman_change.log’;

Database altered.

This command creates a binary file
called /rman_bkups/change.log for tracking purposes.

To see whether change tracking is currently enabled, you can query:

SQL> select filename, status from v$block_change_tracking;

FILENAME STATUS
————— ————

 

Conversely, you can disable tracking with

 SQL> alter database disable block change tracking;

Database altered.

To see whether change tracking is currently enabled, you can query:

SQL> select filename, status from v$block_change_tracking;

FILENAME       STATUS
----------     -------