Oracle -RMAN Block Change Tracking
With Oracle 10gr1 Enterprise Edition Oracle introduce Block change tracking feature which use to FAST / Speed up RMAN Incremental Backup.
What is BLOCK CHANGE TRACKING in RMAN:
RMAN's 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 datafile.
After enabling change tracking, the first level 0 incremental backup still has to scan the entire datafile, as the change tracking file does not yet reflect the status of the blocks. Subsequent incremental backup that use this level 0 as parent will take advantage of the change tracking file.
Source: Oracle documentation
1. Enable Block Change tracking and set location
Before enabling we must to set/specify block change tracking location.There is two way to specify block change tracking location1. using DB_CREATE_FILE_DEST parameter which use OMF file name.
SQL> alter system set db_create_file_dest='location' SCOPE=BOTH;
SQL> alter database enable block change tracking;
2. Manually specify location for the block change tracking
SQL>alter database enable block change tracking using file 'location';
2. Disable block change tracking
SQL> alter database disable block change tracking;
NOTE: BCT files deleted automatically by oracle when BCT is disabled.
3. Reset the location of Block change tracking file
-There are two options for this
1. shutdown the database and set the new location
SQL> shutdown database
SQL> move BCT file to new location
SQL> startup mount
SQL> alter database rename file 'old_location' TO 'new_location';
SQL> alter database open;
or
2. disable the block change tracking / set the new location / enable BCT
SQL> alter database DISABLE block change tracking;
SQL> alter database enable block change tracking using FILE 'NEW_LOCATION';
After that RMAN use new location for the BCT.
4. Checking the information about block change tracking enable or disable
Check v$BLOCK_CHANGE_TRACKING view
5. BCT file is important for restore and recovery of database.
Answer: No, it is doesn't require for Database Recovery of database
-What happen if BCT file is lost and corrupted.
That is very interesting case here, suppose oracle found if BCT file is corrupted or missing then oracle will automatically recreate new BCT file.
Let see some practical...
1. Enable BCT
SQL> alter database enable block change tracking using file 'e:\bct.dbf';
Database altered.
2. Check the status and default size.
SQL> select * from v$block_change_tracking;
STATUS FILENAME BYTES
--------------------------------- ----------
ENABLED E:\BCT.DBF 11599872
NOTE: Filesize created is 11 mb by default.
3. Now check alertsid log file what entries we found.
alter database enable block change tracking using file 'e:\bct.dbf'
Block change tracking file is current.
Starting background process CTWR
Mon Jul 28 20:06:54 2008
CTWR started with pid=20, OS id=464
Block change tracking service is active.
Completed: alter database enable block change tracking using file 'e:\bct.dbf'
4. Disable BCT
SQL> alter database disable block change tracking;
Database altered.
SQL> select * from v$block_change_tracking;
STATUS FILENAME BYTES
---------- ---------------------------------------- ----------
DISABLED
5. Check alertlog file
Mon Jul 28 20:12:41 2008
alter database disable block change tracking
Mon Jul 28 20:12:41 2008
Block change tracking service stopping.
Stopping background process CTWR
Deleted file E:\BCT.DBF
Completed: alter database disable block change tracking
6. Suppose BCT file lost or missing then what oracle will do...
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> host del c:\bct.dbf
SQL> startup
ORACLE instance started.
Database mounted.
Database opened.
Now check the alertlog file for more information about how oracle create new BCT file when missing or lost.
Mon Jul 28 20:16:54 2008
ALTER DATABASE OPEN
CHANGE TRACKING is enabled for this database, but the change tracking file can not be found. Recreating the file.
Change tracking file recreated.
Block change tracking file is current.
With Oracle 10gr1 Enterprise Edition Oracle introduce Block change tracking feature which use to FAST / Speed up RMAN Incremental Backup.
What is BLOCK CHANGE TRACKING in RMAN:
RMAN's 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 datafile.
After enabling change tracking, the first level 0 incremental backup still has to scan the entire datafile, as the change tracking file does not yet reflect the status of the blocks. Subsequent incremental backup that use this level 0 as parent will take advantage of the change tracking file.
Source: Oracle documentation
1. Enable Block Change tracking and set location
Before enabling we must to set/specify block change tracking location.There is two way to specify block change tracking location1. using DB_CREATE_FILE_DEST parameter which use OMF file name.
SQL> alter system set db_create_file_dest='location' SCOPE=BOTH;
SQL> alter database enable block change tracking;
2. Manually specify location for the block change tracking
SQL>alter database enable block change tracking using file 'location';
2. Disable block change tracking
SQL> alter database disable block change tracking;
NOTE: BCT files deleted automatically by oracle when BCT is disabled.
3. Reset the location of Block change tracking file
-There are two options for this
1. shutdown the database and set the new location
SQL> shutdown database
SQL> move BCT file to new location
SQL> startup mount
SQL> alter database rename file 'old_location' TO 'new_location';
SQL> alter database open;
or
2. disable the block change tracking / set the new location / enable BCT
SQL> alter database DISABLE block change tracking;
SQL> alter database enable block change tracking using FILE 'NEW_LOCATION';
After that RMAN use new location for the BCT.
4. Checking the information about block change tracking enable or disable
Check v$BLOCK_CHANGE_TRACKING view
5. BCT file is important for restore and recovery of database.
Answer: No, it is doesn't require for Database Recovery of database
-What happen if BCT file is lost and corrupted.
That is very interesting case here, suppose oracle found if BCT file is corrupted or missing then oracle will automatically recreate new BCT file.
Let see some practical...
1. Enable BCT
SQL> alter database enable block change tracking using file 'e:\bct.dbf';
Database altered.
2. Check the status and default size.
SQL> select * from v$block_change_tracking;
STATUS FILENAME BYTES
--------------------------------- ----------
ENABLED E:\BCT.DBF 11599872
NOTE: Filesize created is 11 mb by default.
3. Now check alertsid log file what entries we found.
alter database enable block change tracking using file 'e:\bct.dbf'
Block change tracking file is current.
Starting background process CTWR
Mon Jul 28 20:06:54 2008
CTWR started with pid=20, OS id=464
Block change tracking service is active.
Completed: alter database enable block change tracking using file 'e:\bct.dbf'
4. Disable BCT
SQL> alter database disable block change tracking;
Database altered.
SQL> select * from v$block_change_tracking;
STATUS FILENAME BYTES
---------- ---------------------------------------- ----------
DISABLED
5. Check alertlog file
Mon Jul 28 20:12:41 2008
alter database disable block change tracking
Mon Jul 28 20:12:41 2008
Block change tracking service stopping.
Stopping background process CTWR
Deleted file E:\BCT.DBF
Completed: alter database disable block change tracking
6. Suppose BCT file lost or missing then what oracle will do...
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> host del c:\bct.dbf
SQL> startup
ORACLE instance started.
Database mounted.
Database opened.
Now check the alertlog file for more information about how oracle create new BCT file when missing or lost.
Mon Jul 28 20:16:54 2008
ALTER DATABASE OPEN
CHANGE TRACKING is enabled for this database, but the change tracking file can not be found. Recreating the file.
Change tracking file recreated.
Block change tracking file is current.
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