Space management in the fast recovery area is governed by a backup retention policy. A retention policy determines when files are obsolete, meaning that they are no longer needed to meet your data recovery objectives.
Retention policies can be based on redundancy of backups or on a recovery window (period of time).
When using a policy based on redundancy, you specify how many full or level 0 backups of each data file and control file that Oracle Recovery Manager (RMAN) keeps. If the number of full or level 0 backups for a specific data file or control file exceeds the redundancy setting, then RMAN considers the extra backups as obsolete.
When using a recovery policy based on a period of time (or window), you specify a time interval in days. Files are obsolete only when they are no longer needed for complete recovery or point-in-time recovery to a system change number (SCN) within the window. Therefore, a recovery retention policy based on a window is recommended.
The default retention policy is a redundancy of 1. Even after files in the fast recovery area are obsolete, they are typically not deleted until space is needed for new files. If space permits, files recently moved to tape remain on disk to avoid restoring them from tape for a recovery. The automatic deletion of obsolete files and files moved to tape from the fast recovery area makes it a convenient archiving destination. Other destinations require manual deletion of logs.
See Also:
Oracle Database Backup and Recovery User's Guide for examples of configuring a redundancy-based policy.