The backup database command backs up all data files and the control file but not the archived redo logs. If you take a consistent backup of the database, you can later use this backup to restore and recover without performing media recovery. That is, you will not have to apply any changes from the archived redo logs before opening the database. To take a consistent backup, you must satisfy the following two conditions: You must first shut down the database normally, that is, use one of the following statements: 1) shutdown, 2) shutdown normal, 3) shutdown immediate, or 4) shutdown transactional.
- You must start up the database in mount state before taking the backup. If you are recovering a database using inconsistent backups, you must first make the database consistent through applying the archived redo logs before you can open it. Backups taken under the following conditions are inconsistent:
- If you create a backup of a database after restarting a database that was shut down abruptly (say, because of a power failure) or with the shutdown abort command
- If you create a backup of the database while the database is open
There is nothing wrong with inconsistent backups by definition, all open database backups are inconsistent.
You can safely use inconsistent backups
as the foundation of your backup and recovery strategy.
Since database uptime is critical, most production databases depend on inconsistent backups.
All you have to do is to make sure you are running your database in archive log mode and that you are backing up your archived redo logs along with your data files.