Improve Incremental Backup Performance -Change Tracking.

RMAN's change tracking feature for incremental backups improves incremental backup performance.
With change tracking feature RMAN creates a file named change tracking file and then any blocks changes entry is recorded in the file.

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. use the change tracking file to identify changed blocks.

Enable and disable Change Tracking
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Block change tracking can enabled by
SQL>ALTER DATABASE ENABLE BLOCK CHANGE TRACKING;
The file will be created in the DB_CRETE_FILE_DEST if it is set. However manually can be set by

SQL>ALTER DATABASE ENABLE BLOCK CHANGE TRACKING USING FILE '/oradata2/change_tracking.f';

To disable change tracking, use this SQL statement:

SQL> ALTER DATABASE DISABLE BLOCK CHANGE TRACKING;

Query V$BLOCK_CHANGE_TRACKING to know the status and filename of block change tracking.