RMAN Block Change Tracking in 19C Database

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Before the start the BCT let’s take quick recap for incremental backup first

Incremental backup

The goal of an incremental backup is to back up only those data blocks that have changed since a previous backup.

During incremental backup, RMAN checks every data block in all datafiles of the database and compares its SCN number with the SCN value that is at the incremental 0 backup.

If the first value is greater than the second, it means that the data block has been changed after the last backup and needs to be backed up, so RMAN writes it to the backup file.

This procedure is done for every data block in the database

So as RMAN checks all data blocks and writes down only changed ones during incremental backup

It takes more time for the checking process so BTC introduced in 10G

Block Change Tracking (BCT)

Oracle 10gR2 database introduced Block change tracking (BTC)

It is used to improve the incremental backup performance by recording changed blocks in each datafile in change tracking file.

Block change tracking provides a way to identify the blocks required for backup without scanning the whole datafile. After that RMAN need only read blocks that are really required for this incremental backup.

Oracle 10g introduces a new special background process Check Tracking Writer (CTWR). This process takes care of logging information about changed blocks in block change tracking file

RAC database, change tracking file is shared amongst all instances.

Default BCT file is created in the location defined by parameter DB_CREATE_FILE_DEST and We can also specify the name of the block change tracking file, placing it in any location.

 

Enable Block Change Tracking: -

Alter database enable block change tracking;

select filename,status from V$BLOCK_CHANGE_TRACKING;

Monitoring Ctwr (change tracking writer process)

select * from v$sgastat where name like '%CTWR%';

select sid,program,status from v$session where program like '%CTWR%';

Disable the Block change track

alter database disable block change tracking; 

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