Your archived redo logs and your backup go hand in hand. Let's say that I backup my database on Saturday. Then the database crashes on Wednesday. In order to restore fully, I need Saturday's backup and all of the archived redo logs since then. So for that reason, I tend to think that the archived redo logs are tied to the backup. Without the backup, the archived redo logs are of little use. And without the archived redo logs, the backup is only as good as the day it was taken.
Many DBAs like to keep multiple backups on hand. We call these generations of backups. The latest backup is generation zero (0). The backup prior to that is generation minus 1 (-1). This type of terminology is from the old mainframe days. Many installations keep many generations available. How many generations? It all depends on the company's policy. Some only keep three generations. Some keep size generations. Some keep enough generations to hold backups for an entire year! It all depends.
I've already discussed how the archived redo logs are "tied" to the backup. If you decide to keep three generations of backups, then you need to keep the archived redo logs for those three backup generations. Once you delete a backup, the archived redo logs from that backup to the next backup are no longer valid. So you can delete those as well.
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This was first published in July 2002