Oracle教程：快照控制檔案

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僅當以下情況下需要快照控制檔案：1.同步恢複目錄時2.對當前控制檔案進行備份時。在RAC環境下，僅僅在實施RMAN備份的節點上需要快照控制檔案;因此快照控制檔案是不需要在所有執行個體上全域可用的。

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

你同樣可以使用共用檔案系統或裸裝置指定快照控制檔案的位置。

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.


如果快照控制檔案配置在共用儲存上時：
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.

這樣看來，每個執行個體使用自己的快照控制檔案可以避免以上問題。

配置執行個體：

[sql]

1. --顯示快照控制檔案位置   
2. RMAN> show snapshot controlfile name;  
3.   
4. RMAN configuration parameters are:  
5. CONFIGURE SNAPSHOT CONTROLFILE NAME TO '/u01/app/oracle/product/10.2.0/db_1/dbs/snapcf_RACDB1.f'; # default  
6.   
7. --配置快照控制檔案位置（使用ASM或共用檔案系統或裸裝置）   
8. RMAN> configure snapshot controlfile name to   
9. '+FRA/SNAP/snap_prod.cf';   
10. RMAN> configure snapshot controlfile name to   
11. '/ocfs/oradata/dbs/scf/snap_prod.cf';   
12. RMAN> configure snapshot controlfile name to '/dev/sdj2';  
13.   
14. --配置快照控制檔案為預設預設值   
15. RMAN> configure snapshot controlfile name clear;  
16.   
17. RMAN configuration parameters are successfully reset to default value