Oracle : Flash Recovery area - Space management Warning & Alerts

Subject:

Flash Recovery area - Space management Warning & Alerts


Doc ID:

Note:305812.1

Type:

BULLETIN


Last Revision Date:

13-JUN-2006

Status:

PUBLISHED



PURPOSE

-------



Flash Recovery area

1. How Oracle Manages Disk Space in the Flash Recovery Area

2. Space management Warning & Alerts

3. Impact of retention policy

4. How to resolve full Flash Recovery Area conditions.





SCOPE & APPLICATION

-------------------

Space management in the Flash Recovery Area for DBAs, support





1. How Oracle Manages Disk Space in the Flash Recovery Area

-----------------------------------------------------------



You can query the V$RECOVERY_FILE_DEST view to find out the current location,

disk quota, space in use, space reclaimable by deleting files, and total

number of files in the Flash Recovery Area.



SQL> SELECT * FROM V$RECOVERY_FILE_DEST;



NAME SPACE_LIMIT SPACE_USED SPACE_RECLAIMABLE NUMBER_OF_FILES

----------- ---------- ----------------- ---------------

D:\Oracle\flash_recovery_area 838860800 292490752 0 44





Oracle does not delete eligible files from the Flash Recovery Area until the

space must be reclaimed for some other purpose. The effect is that files

recently moved to tape are often still available on disk for use in recovery.

The recovery area can thus serve as a kind of cache for tape. Once the Flash

Recovery Area is full, Oracle automatically deletes eligible files to reclaim

space in the Flash Recovery Area as needed.



The following rules apply for files to become eligible for

deletion from the Flash Recovery Area:

- Files that are obsolete under the configured retention policy

- Transient files that have been copied to tape.

- In a Data Guard environment, archived redolog deletion policy governs when

archived redolog files can be deleted from the Flash Recovery Area.



- Permanent files are never eligible for deletion.





2. Flash Recovery area - Space management Warning & Alerts

----------------------------------------------------------



The database issues a warning alert when reclaimable space is less than 15%

and a critical alert when reclaimable space is less than 3%. To warn the DBA

of this condition, an entry is added to the alert log and to the

DBA_OUTSTANDING_ALERTS table (used by Enterprise Manager). However, the

database continues to consume space in the Flash Recovery Area until there is

no reclaimable space left. When the Flash Recovery Area is completely full, the

following error will be reported:



ORA-19809: limit exceeded for recovery files

ORA-19804: cannot reclaim bytes disk space from limit



where is the number of bytes required and is the disk quota for

the Flash Recovery Area.



The following Error would be reported in alert.log

ORA-19815: WARNING: db_recovery_file_dest_size of

bytes is 100.00% used, and has 0 remaining bytes available.



Issue the following query to see the message:



SQL> SELECT object_type, message_type, message_level,

reason, suggested_action

FROM dba_outstanding_alerts;



The following actions can be done to resolve the space issue :

- Add disk space to the Flash Recovery Area.

- Back up your files to a tertiary device.

- Delete the files from the Flash Recovery Area using RMAN.

- Changing RMAN retention policy.



The database handles a Flash Recovery Area with insufficient reclaimable space

just as it handles a disk full condition. Often, the result is a hang of the database.





3. Retention Policy / Obsolete Files in Flash Recovery Area

-----------------------------------------------------------



Correct use of a Flash Recovery Area, requires a retention policy. No retention

policy will cause files in the Flash Recovery Area never become obsolete, causing

major issues on the database.



The RMAN status OBSOLETE is always determined in reference to a retention

policy. For example, if a database backup is OBSOLETE in the RMAN repository,

it is because it is either not needed for recovery to a point within the

recovery window, or it is redundant.



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.



A safe and reliable way to control deletion of files from the Flash Recovery

Area is to change the retention policy.





4. Resolving a Full Flash Recovery Area

---------------------------------------



There are a number of choices on how to resolve a full Flash Recovery Area when

there are NO files eligible for deletion:

- Make more disk space available, and increase DB_RECOVERY_FILE_DEST_SIZE

to reflect the new space.



SQL> alter system set DB_RECOVERY_FILE_DEST_SIZE= ;



- Use the command BACKUP RECOVERY AREA, to back up the contents of the

Flash Recovery Area to a tertiary device such as tape.



Example:

RMAN> backup device type 'sbt_tape' recovery area;



- Delete unnecessary files from the Flash Recovery Area using the RMAN delete

command.



NOTE: If a host operating system command is used to delete files,

then the database will not be aware of the resulting free space. Run

the RMAN CROSSCHECK command to have RMAN re-check the contents of the

Flash Recovery Area and identify the deleted files. Afterwards run DELETE

EXPIRED to remove deleted files from the RMAN repository.



- You may also need to consider changing your backup retention policy



Example :

RMAN> configure retention policy to recovery window of 30 days;



- When using Data Guard, consider changing your archivelog deletion policy.





REFERENCE

Note 305817.1 FAQ - Flash Recovery Area feature of 10G

Reference : http://umardba.blogspot.com/2009/12/flash-recovery-area-space-management.html