Incomplete recovery of data is referred as incomplete recovery because only a part of logs i.e redo logs, archive log data are applied to a backup to bring the system back to a specified time, sequence number or check point number.Database must be present in ARCHIVELOG mode to perform an incomplete recovery. Following situation may require to perform an incomplete recovery :
Complete recovery has failed to some reason.
You do want to restore all data due to user errors or you want to create a test or standby database.
You have lost online redo logs or archive logs.
Incomplete recovery can be done using following :
Time based incomplete recovery : Recovers the data up to a specified point in time. It is used when
- Bad data was committed to the database; or
- Important data was dropped. To minimize the data loss and recovery time, the DBA should be notified immediately after the user error occurs.
- You know the approximate time when a non-mirrored online redo log becomes corrupt.
Change based incomplete recovery : Recovers until the specified SCN. It is used when
- Redo log file or group is lost.
- archived logs needed for recovery are lost.
Cancel based incomplete recovery: recovers until you issue the CANCEL statement (not available when using Recovery Manager).
- You are recovering a database in a distributed environment.
Log sequence recovery : recovers until the specified log sequence number (only available when using Recovery Manager).
- You lose all the current control files. You cannot recreate the control file, but you have the backup of the older control file.
- There is a need to restore the database to a certain point in time with a structure different from the current one.
Though, it depends on the situation and various parameters but if possible, Time based recovery provides most fine control for the recovery.
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