Tales From A Lazy Fat DBA

Even after a good Database Upgrade plan one can face issues related to performance, Functionailities, Backups etc. Today I’m going to discuss one of the case that was happened during a production upgrade from 10g r2 -> 11g r2.

We had our database full backup scheduled every night with configuration like – Autobackup ON, Dataa transfer directly to SBT Mediums (Tapes), OPTIMIZATION ON and other basic settings/configurations.
While performing status check next morning we discovered backup got failed with error message:

ORA-00245: control file backup failed; target is likely on a local file system

Error
———
Starting Control File and SPFILE Autobackup at 2013-09-06:21:25:34
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03009: failure of Control File and SPFILE Autobackup command on ORA_SBT_TAPE_1 channel at 09/06/2013 21:25:36
ORA-00245: control file backup failed; target is likely on a local file system

As we have AUTOBACKUP functionailty ON which takes backup of critical files like controlfile file whenever the database structure metadata in the control file changes and whenever a backup record is added.

Reason:
Fro 11gR2 onwards in RAC database, due to the changes made to the controlfile backup mechanism, any instance in the cluster may write to the snapshot controlfile. Due to this snapshot controlfile need to be visible to all instances.
A snapshot controlfile in 11gr2 must be reachable by all nodes in RAC Environment. If the snapshot controlfile is not available or not shared RMAN will throw such errors during backup operations.
Documentation Link: http://docs.oracle.com/cd/E11882_01/rac.112/e16795/rman.htm#i455026

Solution:
To avoid such situations always keep your snapshot controlfile on a shared location so that it could be accessible by all nodes when needed.

RMAN> configure snapshot controlfile name to ‘/disk02/rmaninfo/snapcontrol/snapcf_cesc1.f’;

using target database control file instead of recovery catalog
new RMAN configuration parameters:
CONFIGURE SNAPSHOT CONTROLFILE NAME TO ‘/disk02/rmaninfo/snapcontrol/snapcf_cesc1.f’;
new RMAN configuration parameters are successfully stored.

Okay now we have the solution of the problem let’s discuss more about Snapshot Controlfile and about this new change in 11g r2.
– When RMAN performs any operation that requires a consistent view of the control file (such as a backup), it will first create a copy of the control file. This copy is called the snapshot control file. The snapshot control file will be used for the duration of that operation and will be overwritten by any subsequent operation. Even related operations (say, during a backup database plus archive-log operation that does an archive log backup, a database backup, and then another archive log backup) will use newly created snapshot control files, one for each operation.

Why and what’s the need of this new change ?
From 11gR2 onwards, the controlfile backup happens without holding the controlfile enqueue.

Now, what’s this ‘ControlFile Enqueue‘ ?
When we need to back up or resynchronize from the Control file by RMAN, that first creates a snapshot or consistent image of the control file.
If one RMAN job is already backing up the control file while another needs to a new snapshot control file, then may see error:

RMAN-08512: waiting for snapshot controlfile enqueue for 1900 seconds

A job that must wait for the control file enqueue waits for a brief interval and then successfully retrieves the enqueue. RMAN makes up to five attempts to get the enqueue and then fails the job. So, finally with oracle 11g r2 we have the solution of this situation (In RAC Env) by keeping snapshot controlfile on shared location.