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The Primary purpose of FRA is to simplify the management of backup and recovery files. The fast recovery area is an Oracle-managed directory, file system, or Oracle Automatic Storage Management disk group that provides a centralized storage location for backup and recovery files. Oracle creates archived logs and flashback logs in the fast recovery area. Oracle Recovery Manager (RMAN) can store its backup sets and image copies in the fast recovery area, and it uses it when restoring files during media recovery. 

Oracle Database automatically manages this storage, deleting files that are no longer needed. Periodically copying backups to tape frees space in the fast recovery area for other files.

When you issue the RMAN BACKUP command without specifying a backup destination, RMAN automatically backs up to the fast recovery area if it is configured.

Below files in the FRA are managed by Oracle and RMAN automatically.  

RMAN backups
control file
logs
online redo log copies
archived redo logs
flashback logs

FRA enhances the space management feature. If Backup files are not configured in FRA, manually removing and managing files will be very risky and tedious job for any DBA.
Assuming that we have FRA configured in enviornment, which is also strongly recommended by Oracle.

So the default behaviour of FRA space management is that it will delete unwanted files when it reaches 85 percent of the total space, to clear the new files to reside . Perhaps, it should satisfy the retention condition defined by RMAN. Lets understand the default behaviour as below screen shot:

As per default behaviour , it will delete once it reaches 85 percent of total space allocated.

However , there could be a situation where you want to change this default percentage behaviour . Let's say, DBA wants to delete the obsoleted files after '39' percent .
This can be changed by setting an event :

alter system set events '19823 trace name context forever, level 39';

*****This will change the reclaimable purging when space limit reaches 39%.

So its clear in alert log that after modifying the threshold value , it started deleting as it reached closede to 39 percent .

Reference:  Flash Recovery area - Space management Warning & Alerts (Doc ID 305812.1)

Happy Learning !!!

Shailesh Singh

DB Alchemist Academy

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