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Change Tracking...
Change tracking eliminates need to read entire file during incremental backup
Notes:
Oracle10g RMAN incremental backups are potentially much faster because the entire datafile does not have to be read to determine which blocks have changed. Instead, the database records (i.e. tracks) changed blocks in a file. When an incremental backup is taken, RMAN accesses the “block change tracking file” to determine which blocks to backup.
In the test shown above, the elapsed time of the level 3 incremental backup is 3 seconds; the same level 3 incremental backup with change tracking disabled required 46 seconds.
This behavior must be configured with the ALTER DATABASE ENABLE BLOCK CHANGE TRACKING statement as shown above. The default location of the block change tracking file is the Oracle Managed File DB_CREATE_FILE_DEST parameter. Use the “FILE” clause if you are not using OMF or you want to put the file in a location other than DB_CREATE_FILE_DEST.
Refer to the Oracle10g SQL Reference for more information on the ALTER DATABASE statement and the Oracle10g Database Backup and Recovery Basics manual for more information on this feature in general.