- Posted by Arjun Raja
- On June 30, 2009
- 1 Comments
BLOCK CHANGE TRACKING
From version 10.2 onwards, Oracle have provided a new tool which is very useful to reduce the time of RMAN incremental backups.
Prior to 10.2, all incremental backups had to read every single block in the database, and if the block has changed, it was backed up. This meant the RMAN backup job took nearly as long as a normal full backup because every block had to be read regardless.
To avoid this, Oracle introduced the BLOCK CHANGE TRACKING file – if this was enabled, then a file called the block change tracking file kept information of all changes to blocks since the last backup. This file was read instead of all the blocks in the database to arrive at changed blocks and then these blocks were backed up.
This reduced the backup time considerably – sometimes, especially in the case of Data Warehouse type databases, since changes happened infrequently, incremental backups hardly took minutes to complete as opposed to many hours.
To enable block change tracking – this can be run with the database open ( as sysdba ).
alter database enable block change tracking using file ‘/hqlinux01db05/ORACLE/test/block_change.dbf’;
select filename,status from v$block_change_tracking;