Files in the recovery area are permanent or transient.
Permanent files are active files used by the database instance (like control files).
All files that are not permanent are transient.
In general, Oracle Database eventually deletes transient files after they become obsolete under the backup retention policy or have been backed up to tape.
Space in the flash recovery area is balanced among backups and archived logs that must be kept according to the retention policy, and other files which may be subject to deletion.
Oracle Database does not delete eligible files from the flash recovery area until the space must be reclaimed for some other purpose.
Thus, files recently moved to tape are often still available on disk for use in recovery. The recovery area can thus serve as a cache for tape.
When the flash recovery area is full, Oracle Database automatically deletes eligible files to reclaim space in the recovery area as needed.
The following rules govern when files become eligible for deletion from the recovery area:
• Permanent files are never eligible for deletion.
• Files that are obsolete under the retention policy are eligible for deletion.
• Transient files that have been copied to tape are eligible for deletion.
• Archived redo logs are not eligible for deletion until all the consumers of the logs have satisfied their requirements. Consumers of logs can include RMAN, standby databases, Oracle Streams databases, and the Flashback Database feature.
The safe and reliable way to control deletion of files from the flash recovery area is to configure your retention policy and archived log deletion policy.
To increase the likelihood that files moved to tape are retained on disk, increase the flash recovery area quota.
Source: Oracle Documentation
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