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Implement Block Change Tracking in Oracle Database



What is Block Change Tracking?

Block Change Tracking is an Oracle Database feature used with RMAN incremental backups. It tracks the physical locations of changed blocks in the database and stores this information in a separate file called the Block Change Tracking file. Oracle documentation states that this tracking information is maintained in a separate file and is used for tasks such as improving incremental backup performance.

Without BCT, RMAN may need to scan the datafiles to determine which blocks have changed since the previous backup. With BCT enabled, RMAN can directly read the change tracking file and identify changed blocks more efficiently.

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Login to SQL

sqlplus / as sysdba


         Set lin 400

SELECT status, filename, bytes

FROM   v$block_change_tracking;


CHECK OMF

SHOW PARAMETER db_create_file_dest; 


ENABLE BCT (BLOCK CHAIN TRACKING)

Common method:

ALTER DATABASE ENABLE BLOCK CHANGE TRACKING; 

Add to a file path:

ALTER DATABASE ENABLE BLOCK CHANGE TRACKING USING FILE '/u01/oradata/DBNAME/bct_file.ctf'; 

Add to ASM

ALTER DATABASE ENABLE BLOCK CHANGE TRACKING USING FILE '+DATA'; 

DISABLE BCT

I have also encountered issues when RMAN restoring and opening database where i used to occur the error that it is unable to find the file for BCT. in such case senario you can drop the database data file with regards to BCT using below command.

ALTER DATABASE DISABLE BLOCK CHANGE TRACKING; 



Advantage of enabling the BCT.

- Faster RMAN incremental backups

BCT helps RMAN quickly identify changed blocks instead of scanning entire datafiles.

- Reduced backup window

Since RMAN reads only the changed block information, incremental backups complete faster, which is useful for large databases.

- Lower I/O during backups

BCT reduces unnecessary datafile scanning, which helps reduce disk I/O and improves overall backup efficiency. 

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