Flash Recovery Area – Size determination

Ideally, the flash recovery area should be large enough to hold a copy of all of your

1. data files
2. control files,
3. the online redo logs
4. the archived redo log files

needed to recover your database using the data file backups kept under your retention policy.
Setting the size of DB_FILE_RECOVERY_DEST_SIZE must be based on following factors.
1) your flash back retention target,
2) what all files you are storing in flashback and
3) if that includes backup then the retention policy for them or how often you move them to tape

Oracle Internal Space management mechanism for Falshback recovery area itself is designed in such way that if you define your db_recovery_file_dest_size and DB_FLASHBACK_RETENTION_TARGET at a optimal value, you wont need any further administration or management.

If a Flash Recovery Area is configured, then the database uses an internal algorithm to delete files from the Flash Recovery Area that are no longer needed because they are redundant, orphaned, and so forth. The backups with status OBSOLETE form a subset of the files deemed eligible for deletion by the disk quota rules.

When space is required in the Flash Recovery Area, then the following files are deleted:
a) Any backups which have become obsolete as per the retention policy.
b) Any files in the Flash Recovery Area which has been already backed up
to a tertiary device such as tape.
c) Flashback logs may be deleted from the Flash Recovery Area to make space available for other required files.