As with 11g Oracle comes with a new feature for Oracle Data Guard: Active Data guard. And with Active Data Guard enabled we can use Block Change Tracking feature for the physical standby database.
Now, what is Block Change Tracking?
Block Change Tracking: RMAN change tracking feature for incremental backups improves incremental backup performance by recording changed blocks in each datafile in a change tracking file. If change tracking is enabled, RMAN uses the change tracking file to identify changed blocks for incremental backup, thus avoiding the need to scan every block in the data file.
With Active Data Guard we can enable block change tracking at Standby side, so when we back up a physical standby database, RMAN will use the block change tracking file to quickly identify the blocks that have changed since last incremental backup.
Follow below steps to enable block change tracking.
Step 1: Checking Database role as we are applying this on a physical standby database.
SQL> select name,open_mode,database_role,db_unique_name from v$database; NAME OPEN_MODE DATABASE_ROLE DB_UNIQUE_NAME --------- -------------------- ---------------- ------------------------------ MGR READ ONLY WITH APPLY PHYSICAL STANDBY std_mgr
Step 2: Check if block change tracking is enabled or not
SQL> select * from v$block_change_tracking; STATUS FILENAME BYTES ---------- -------------------- ---------- DISABLED
Step 3: Check if OMF is enabled or not.
SQL> show parameter db_create_file_Dest NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ db_create_file_dest string
In this case, OMF is not enabled. If OMF is enabled we just need to write ALTER DATABASE ENABLE BLOCK CHANGE TRACKING; and then BCT file will be created to the destination we have specified in the db_create_file_dest parameter.
But here we need to enable it by specifying using clause.
SQL> ALTER DATABASE ENABLE BLOCK CHANGE TRACKING USING FILE '/u01/oracle/oradata/bct_mgr.f'; Database altered. SQL>
We can see in alert log file CTWR background process associated with BCT is started.
ALTER DATABASE ENABLE BLOCK CHANGE TRACKING USING FILE '/u01/oracle/oradata/bct_mgr.f' Block change tracking file is current. Starting background process CTWR Wed May 09 22:21:01 2018 CTWR started with pid=39, OS id=4099 Block change tracking service is active. Completed: ALTER DATABASE ENABLE BLOCK CHANGE TRACKING USING FILE '/u01/oracle/oradata/bct_mgr.f'
Note: We can not enable Block Change Tracking for standby database which does not have Active Data guard option enabled, because Block Change Tracking need database opened in read-write mode or read-only mode and it can not work if your database is just mounted.
Stay tuned for More articles on Oracle DataGuard
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