Author: K. Burleson

Even Oracle qualified DBAs flinch at the thought of performing a real-world database recovery. As disk and hardware has become super-stable, many Oracle DBAs have never experienced the adrenaline rush of a full-scale Oracle recovery.

With a mission decisive database at risk, these Oracle recoveries are often performed under great stress, especially when thousands of employees cannot do their jobs until you have recovered their Oracle system.

I am amazed how many Oracle shops do not discover that their backups are bad until they are doing a mission-critical recovery. The most common causes of backup include:

Back up strategy:

Cold backups while the database is running are a very common Oracle backup error. When you reinstate the media, Oracle will not open the database because the system change numbers (SCN) in the file headers do not match.

Improper Media:

Many Oracle backups do not check the media to ensure that the database has been successfully written to the backup tape or disk. I have seen many cases where the backup writes and empty of incomplete backup, or where equivalence checks exist. Some shops re-read their backups to ensure against uniformity errors.

Not attempting Roll-Forward:

I have seen many shops that only discover that they cannot roll-forward until they attempt a recovery. Many DBAs have lost their jobs when they must tell management that many days of work has been lost forever.

Improper hot backups:

There are many ways to perform a hot backup, and many of them will not work properly. Hot backups are complicated, and the cautious DBA will insist that the recovery from the hot backup is tested, or at least get a CYI memo from management if they reject to test their Oracle recovery capabilities. Remember, someone is going to be fired when a mission-critical database cannot be restored, and this memo could save your job.

There are also areas of Oracle database recovery where the DBA could make a serious error. These mistakes are often the result of stress and poor judgment, and even Oracle Technical Support may fail to be adamant of these precautions. Here are two common Oracle recovery issues to avoid:

Back-up corrupt database:

The very first task of an Oracle DBA should be to back-up the corrupt database. Sadly, many Oracle shops do not test their recoveries, and in cases where you discover that your backups are not recoverable, you may be glad that you have a copy of the original corrupt database.

Opening corrupt database:

When an Oracle database recovery is corrupt the Oracle database will not open. This is for a good reason and it is Oracle's way of preventing the serious problems of having to manually revamp thousands of corrupt database blocks. When a recovered database will not open you have three choices:  

Roll forward phase:

It is far better to have a longer roll-forward phase than to have to repair Oracle corruption.

Restoring corrupted database :

This may have less manual repair time than forcing open a bad recovery.

Force-open the database :

It amazes me how many Oracle DBAs will have a failed recovery and call Oracle Technical Support asking them to force-open the database without considering other options. Forcing-open a corrupt database is a last-resort and should only be done with the help of Oracle Technical Support and when there are no other options. At this point in time, many Oracle DBAs will realize that they are going to be fired anyway, and walk off the job.

Final Thoughts:

In sum, the Oracle DBA is the guardian of the database and they must be careful and cautious with their mission-critical system and always follow best-practices to make sure recoverability of the Oracle system.

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