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

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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

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  Space management in the Flash Recovery Area  for DBAs, support 

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

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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 

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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

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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

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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

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Note 305817.1 FAQ - Flash Recovery Area feature of 10G