In backup undo optimization, RMAN excludes undo not needed for recovery from the backup, that is, for transactions which have already been committed. For example, a user updates the salaries table in the USERS tablespace. The change is written to the USERS tablespace, while the before image of the data is written to the UNDO tablespace. The user commits. A subsequent RMAN backup of the UNDO tablespace does not include the undo information for the salary changes as a restore of this backup would already have the committed data.
The undo excluded is based on commit of user and an internally specified period of time. Backup undo optimization is built-in RMAN behavior. However, there are some restrictions:
- Compatible parameter must be set to 11.0 or higher
- Backup must use a disk or OSB channel
- For ‘backup copy of [object]’ or ‘backup datafilecopy’ the database must be open for undo optimization to be used.
- Not active for LEVEL 1 incremental backups, only for LEVEL 0 and FULL backups
RMAN> list backup of datafile 3; List of Backup Sets =================== BS Key Type LV Size Device Type Elapsed Time Completion Time ------- ---- -- ---------- ----------- ------------ --------------- 58 Full 73.10M DISK 00:00:29 14-JAN 00:07:00 BP Key: 69 Status: AVAILABLE Compressed: NO Tag: TAG20070114T000631 Piece Name: [name of backuppiece name] List of Datafiles in backup set 58 File LV Type Ckp SCN Ckp Time Name ---- -- ---- ---------- --------------- ---- 3 Full 277406 14-JAN 00:06:31 /[path]/undotbs01.dbf
RMAN> backup datafile 3; Starting backup at 14-JAN 00:07:44 using channel ORA_DISK_1 using channel ORA_DISK_2 channel ORA_DISK_1: starting full datafile backup set channel ORA_DISK_1: specifying datafile(s) in backup set input datafile file number=00003 name=[path]/undotbs01.dbf channel ORA_DISK_1: starting piece 1 at 14-JAN 00:07:45 channel ORA_DISK_1: finished piece 1 at 14-JAN 00:07:48 piece handle=/[name of backuppiece] tag=TAG20070114T000744 comment=NONEchannel ORA_DISK_1: backup set complete, elapsed time: 00:00:03 Finished backup at 14-JAN 00:07:48 Starting Control File and SPFILE Autobackup at 14-JAN 00:07:48 piece handle=[name of controlfile backuppiece] comment=NONE Finished Control File and SPFILE Autobackup at 14-JAN 00:07:50
RMAN> list backup of datafile 3; List of Backup Sets =================== BS Key Type LV Size Device Type Elapsed Time Completion Time ------- ---- -- ---------- ----------- ------------ --------------- 58 Full 73.10M DISK 00:00:29 14-JAN 00:07:00 BP Key: 69 Status: AVAILABLE Compressed: NO Tag: TAG20070114T000631 Piece Name: [name of backuppiece] List of Datafiles in backup set 58 File LV Type Ckp SCN Ckp Time Name ---- -- ---- ---------- --------------- ---- 3 Full 277406 14-JAN 00:06:31 /[path]/undotbs01.dbf BS Key Type LV Size Device Type Elapsed Time Completion Time ------- ---- -- ---------- ----------- ------------ --------------- 61 Full 12.60M DISK 00:00:02 14-JAN 00:07:47 BP Key: 72 Status: AVAILABLE Compressed: NO Tag: TAG20070114T000744 Piece Name: [name of backuppiece] List of Datafiles in backup set 61 File LV Type Ckp SCN Ckp Time Name ---- -- ---- ---------- --------------- ---- 3 Full 277477 14-JAN 00:07:45 /[path]/undotbs01.dbf BS Key Type LV Size Device Type Elapsed Time Completion Time ------- ---- -- ---------- ----------- ------------ --------------- 63 Full 536.00K DISK 00:00:01 14-JAN 00:51:05 BP Key: 74 Status: AVAILABLE Compressed: NO Tag: TAG20070114T005104 Piece Name: [name of backuppiece] List of Datafiles in backup set 63 File LV Type Ckp SCN Ckp Time Name ---- -- ---- ---------- --------------- ---- 3 Full 278620 14-JAN 00:51:04 /[path]/undotbs01.dbf