【Oracle】DG中 Switchover 主、备切换

操作系统：OEL 5.6

数据库版本：Oracle11gR2  11.2.0.4.0

Switchover切换要求主库和备库在数据同步情况下进行，是主备之间的正常切换，主要用于日常维护、灾备演练等。切换顺序为主库先切换为新备库，然后原备库再切换为新主库。

1.通过V$DATABASE查看主库的DATABASE_ROLE、SWITCHOVER_STATUS

##SWITCHOVER_STATUS为TO STANDBY、SESSIONS ACTIVE 均是满足要求状态。

SQL> SELECT OPEN_MODE,SWITCHOVER_STATUS FROM V$DATABASE;

OPEN_MODE            SWITCHOVER_STATUS

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

READ WRITE           TO STANDBY

2.对主库进行切换

SQL> ALTER DATABASE COMMIT TO SWITCHOVER TO PHYSICAL STANDBY WITH SESSION SHUTDOWN;

Database altered.

3.启动原主库到MOUNTED状态

SQL> STARTUP MOUNT;

ORACLE instance started.

Total System Global Area  835104768 bytes

Fixed Size     2257840 bytes

Variable Size   536874064 bytes

Database Buffers   289406976 bytes

Redo Buffers     6565888 bytes

Database mounted.

4.查询转换后的DATABASE_ROLE、SWITCHOVER_STATUS

SQL> SELECT OPEN_MODE,SWITCHOVER_STATUS FROM V$DATABASE;

OPEN_MODE            SWITCHOVER_STATUS

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

MOUNTED              RECOVERY NEEDED

5.查看原备库的DATABASE_ROLE、SWITCHOVER_STATUS

##SWITCHOVER_STATUS为TO PRIMARY、SESSIONS ACTIVE 均是满足要求状态。

SQL> SELECT OPEN_MODE,SWITCHOVER_STATUS FROM V$DATABASE;

OPEN_MODE            SWITCHOVER_STATUS

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

READ ONLY WITH APPLY TO PRIMARY

6.对原备库进行切换

SQL> ALTER DATABASE COMMIT TO SWITCHOVER TO PRIMARY WITH SESSION SHUTDOWN;

Database altered.

7.打开转换后的新主库

SQL> ALTER DATABASE OPEN;

Database altered.

8.对转换后的新备库应用日志

SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE USING CURRENT LOGFILE DISCONNECT FROM SESSION;

Database altered.

9.查看新主库、新备库状态

SQL> SELECT OPEN_MODE,SWITCHOVER_STATUS FROM V$DATABASE;

OPEN_MODE            SWITCHOVER_STATUS

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

READ WRITE           TO STANDBY

SQL> SELECT OPEN_MODE,SWITCHOVER_STATUS FROM V$DATABASE;

OPEN_MODE            SWITCHOVER_STATUS

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

MOUNTED              NOT ALLOWED

至此，Switchover切换完成！

总结：Switchover为主、备之间的正常切换，切换前要保证主、备库的数据一致，而且要先主切备，后备切主，避免同时存在两个主库。