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Note: Once enabled; this new 10g feature records the modified since last backup and stores the log of it in a block change tracking file using the CTW (Change Tracking Writer) process.
During backups RMAN uses the log file to identify the specific blocks that must be backed up. This improves RMAN's performance as it does not have to scan whole datafiles to detect changed blocks.
Logging of changed blocks is performed by the CTRW process which is also responsible for writing data to the block change tracking file.
You can only enable block change tracking at a physical standby database if a license for the Oracle Active Data Guard option has been purchased and this option is enabled.
To enable Active Data Guard on a standby database, set the ENABLE_OPTION_ACTIVE_DATA_GUARD initialization parameter to TRUE.
If a license for the Data Guard option has not been purchased, the ENABLE_OPTION_ACTIVE_DATA_GUARD initialization parameter should be set to FALSE.
The open standby database will be closed, if recovery is started, and the following message is displayed in the alert log:
You have note enabled the Active Data Guard option by setting ENABLE_OPTION_ACTIVE_DATA_GUARD to TRUE. The standby database will be closed before starting recover.
DISABLE
Disable block change tracking
ALTER DATABASE DISABLE BLOCK CHANGE TRACKING;
conn / as sysdba
SELECT filename, status, bytes
FROM v$block_change_tracking;
ALTER DATABASE DISABLE BLOCK CHANGE TRACKING;
SELECT filename, status, bytes
FROM v$block_change_tracking;
SELECT *
FROM gv$sgastat
WHERE name LIKE '%CTWR%';
SELECT inst_id, sid, program, status
FROM gv$session
WHERE program LIKE '%CTWR%';
ENABLE
Enable block change tracking
ALTER DATABASE ENABLE BLOCK CHANGE TRACKING [USING FILE <file_path_and_name>] [REUSE];
conn / as sysdba
SQL>
col filename format a60
SQL> SELECT filename, status, bytes
2 FROM v$block_change_tracking;
FILENAME STATUS BYTES
------------------------------------------------------ ---------- ----------
DISABLED
SQL>
ALTER DATABASE ENABLE BLOCK CHANGE TRACKING
2 USING FILE '/u01/app/oracle/fast_recovery_area/ORABASE/bctf01.log';
Database altered.
SQL> SELECT filename, status, bytes
2 FROM v$block_change_tracking;
FILENAME STATUS BYTES
------------------------------------------------------ ---------- ---------
/u01/app/oracle/fast_recovery_area/ORABASE/bctf01.log ENABLED 11599872
SQL>
SELECT *
2
FROM gv$sgastat
3
WHERE name LIKE '%CTWR%';
INST_ID POOL NAME BYTES CON_ID
---------- -------------- ---------------- -------- -------
1 large pool CTWR dba buffer 1015808 1
SQL>
SELECT inst_id, sid, program, status
2
FROM gv$session
3
WHERE program LIKE '%CTWR%';
INST_ID SID PROGRAM STATUS
-------- ---- ------------------------- -------
1 189 oracle@db18c-ee-hp (CTWR) ACTIVE
