Unix Backup and Recovery

Managing the Archived Redologs

How common is the question, “Should I have archiving turned on?” Yes, yes, a thousand times yes ! When in doubt, archive it out! Here’s what is possible only if archiving is enabled:

• Recover up to the point of failure.

• Recover from a backup that is a month or more old—if all the archived redologs since then are available.

• Perform a complete backup of the database without even shutting it down.

The existence of archive logs does all this without adding significant overhead to the entire process. The only difference between having archiving on or off is whether or not Oracle copies the current redolog out to disk when it “switches” from one redolog to the next. That’s because even with archiving off, it still logs every transaction in the online redologs. That means that the only overhead associated with archiving is the overhead associated with copying the online file to the archive location, which is why there may be only a 1-3 percent performance hit in an environment with many transactions—if there is one at all. Feel free to experiment, but it is very difficult to justify turning off archiving on any production database.

Archiving Saves the Day

I know of one company that had a 250-GB database that did not use archiving at all. The biggest downside to this was that they could not do hot backups, and a cold backup took too long. The result was that they didn’t do any backups! The DBAs didn’t want to turn on archiving because they said that it would make ...