Databases Reference
In-Depth Information
Complete database recovery
If the database did not archive redo logs, only a complete closed backup is possible.
Correspondingly, only a complete database recovery can be performed. You restore
the database files, redo logs, and control and server parameter files from the backup.
The database is essentially restored as of the time of the backup. All work done since
the time of the backup is lost and a complete recovery must be performed even if
only one of the datafiles is damaged. The potential for lost work, coupled with the
need to restore the entire database to correct partial failure, are reasons most shops
avoid this situation by running their databases in ARCHIVELOG mode.
Figure 11-8
illustrates backup and recovery for an Oracle Database without ar‐
chived redo logs.
Figure 11-8. Database backup and recovery without archived redo logs
Partial or targeted restore and roll forward recovery
When you're running the Oracle database in ARCHIVELOG mode, you can restore
only the damaged datafile(s) and can apply redo log information from the time the
backup was taken to the point of failure. The archived and online redo logs repro‐
duce all the changes to the restored datafiles to bring them up to the same point in
time as the rest of the database. This procedure minimizes the time for the restore
and recovery operations. Partial recovery like this can be done with the database
down. Alternatively, the affected tablespace(s) can be placed offline and recovery
can be performed with the rest of the database available. You can also restore and
recover individual data blocks instead of entire datafiles.
Figure 11-9
illustrates
backup and recovery with archived redo logs.
