Oracle Tutorial: Snapshot Control File

ThesnapshotcontrolfileisatemporarysnapshotcontrolfilethatRMANcreatestore-synchronizefromaread-consisten

The snapshot control file is a temporary snapshot control file that RMAN creates to re-synchronize from a read-consisten

The snapshot control file is a temporary snapshot control file that RMAN creates to re-synchronize from a read-consistent version of the control file. RMAN only needs a snapshot control file when re-synchronizing with the recovery catalog or when making a backup of the current control file. in Oracle RAC, the snapshot control file is only needed on the nodes on which RMAN performs backups; the snapshot control file does not need to be globally available to all instances in an Oracle RAC environment.

RMAN only needs snapshot control files in the following situations: 1. When the directory is synchronized to restore 2. When the current control file is backed up. In the RAC environment, snapshot control files are only required for nodes that implement RMAN backup. Therefore, snapshot control files do not need to be globally available on all instances.

You can specify a cluster file system file or a raw device destination for the location of your snapshot control file.

You can also use the shared file system or bare device to specify the location of the snapshot control file.

Run the following RMAN command to determine the configured location of the snapshot control file:

Show snapshot controlfile name;

You can change the configured location of the snapshot control file. for example, on UNIX-based systems you can specify the snapshot control file location as $ ORACLE_HOME/dbs/scf/snap_prod.cf by entering the following at the RMAN prompt:

Configure snapshot controlfile name to '$ ORACLE_HOME/dbs/scf/snap_prod.cf ';

This command globally sets the configuration for the location of the snapshot control file throughout your cluster database. Therefore, ensure that the directory $ ORACLE_HOME/dbs/scf exists on all nodes that perform backups.


If the snapshot control file is configured on shared storage:
If one RMAN job is already backing up the control file while another needs to create a new snapshot control file, you may see the following message:

Waiting for snapshot control file enqueue

Under normal circumstances, a job that must wait for the control file enqueue waits for a brief interval and then successfully retrieves the enqueue. recovery Manager makes up to five attempts to get the enqueue and then fails the job. the conflict is usually caused when two jobs are both backing up the control file, and the job that first starts backing up the control file waits for service from the media manager.

In this way, each instance can use its own snapshot control file to avoid the above problems.

Configuration instance:

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