All data is recovered to the time of failure, so no committed data is lost. Applying archived and redo logs to the restored file brings the database to the current point in time.
The total recovery time is equal to the time your disk can restore the required files plus apply all archived and redo logs.
Recovery can be performed while the database is open for access. However, the database cannot be recovered in open mode if the SYSTEM tablespace or datafiles containing online rollback segments need to be recovered.
All archived logs from the time of your last backup to the current time must be available because all archives need to be applied in sequence.
If one log is missing, a complete recovery becomes impossible.
You can recover only up to the point of the missing archive log.
Routine closed whole database backups of the ARCHIVELOG database are recommended.
Recovering from Failures
Despite the prevalence of redundant or protected disk storage, media failures can and do occur. In cases in which one or more Oracle datafiles are lost due to disk failure,
you must use database backups to recover the lost data. There are times when simple human or machine error can also lead to the loss of data, just as a media failure can. For example, an administrator may accidentally delete a datafile, or an I/O subsystem may malfunction, corrupting data on the disks. The key to being prepared to handle these types of failures is implementing a good backup-and-recovery strategy and understanding the power of Oracle's newer features such as Flashback.
This diagram shows the recovery time for 1) Flashback versus 2) Traditional Recovery
Flashback revolutionizes error recovery
View "good" data as of a past point-in-time
Simply rewind data changes
Time to correct error equals time to make error
Correction Time = Error Time
Low impact
Excellent tool for configuring QA, Dev and Training databases
Flashback is easy – simple commands, no complex procedure
Developing a Backup-and-Recovery Strategy
Proper development, documentation, and testing of your backup-and-recovery strategy is one of the most important activities in implementing an Oracle database.
You must test every phase of the backup-and-recovery process to ensure that the entire process works, because once a disaster hits, the complete recovery process must work flawlessly.
Some companies test the backup procedure but fail to actually test recovery using the backups taken. Only when a failure requires the use of the backups do companies discover that the backups in place were unusable
for some reason. It is critical to test the entire cycle from backup through restore and recovery.