Oracle DataGuard主备切换可以使用传统的手动命令切换，也可以使用dgmgr切换，本文记录手动切换。

(一)将主库切换为物理备库

STEP1：查看主库状态

SQL>  SELECT OPEN_MODE, DATABASE_ROLE, SWITCHOVER_STATUS, FORCE_LOGGING, DATAGUARD_BROKER, GUARD_STATUS FROM V$DATABASE;

OPEN_MODE            DATABASE_ROLE    SWITCHOVER_STATUS    FOR DATAGUAR GUARD_S
-------------------- ---------------- -------------------- --- -------- -------
READ WRITE           PRIMARY          SESSIONS ACTIVE      YES DISABLED NONE

注意：需要检查SWITCHOVER_STATUS参数，如果值为”SESSION ACTIVE”或者”TO STANDBY”, 则主数据库角色可以切换为备库角色。

STEP2：将其切换到备库，切换后，数据库会关闭

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

注意：如果上一步的SWITCH_STATUS参数值为”TO STANDBY”，则 WITH SESSION SHUTDOWN 可以省略。

STEP3：启动到mount状态

SQL> SHUTDOWN ABORT
SQL> STARTUP MOUNT

注意：11.2.0.4版本及其以上版本不需要执行”SHUTDOWN ABORT”，因为数据库已经在STEP2命令中关闭了。

(二) 将备库切换成主库并启动到open
STEP1：查看备库状态

SQL> SELECT OPEN_MODE, DATABASE_ROLE, SWITCHOVER_STATUS, FORCE_LOGGING, DATAGUARD_BROKER, GUARD_STATUS FROM V$DATABASE;

OPEN_MODE            DATABASE_ROLE    SWITCHOVER_STATUS    FOR DATAGUAR GUARD_S
-------------------- ---------------- -------------------- --- -------- -------
READ ONLY WITH APPLY PHYSICAL STANDBY TO PRIMARY           YES DISABLED NONE

注意：需要检查SWITCH_STATUS参数，如果值为”SESSION ACTIVE”或”TO PRIMARY”，则备库可以切换为主库。

STEP2： 切换到主库

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

注意：如果上一步的SWITCH_STATUS参数值为”TO PRIMARY”，则 WITH SESSION SHUTDOWN 可以省略。

STEP3： 此时数据库为mount状态，需打开数据库

SQL> SELECT OPEN_MODE, DATABASE_ROLE, SWITCHOVER_STATUS, FORCE_LOGGING, DATAGUARD_BROKER, GUARD_STATUS FROM V$DATABASE;

OPEN_MODE            DATABASE_ROLE    SWITCHOVER_STATUS    FOR DATAGUAR GUARD_S
-------------------- ---------------- -------------------- --- -------- -------
MOUNTED              PRIMARY          NOT ALLOWED          YES DISABLED NONE

SQL> ALTER DATABASE OPEN ;

Database altered.

SQL>  SELECT OPEN_MODE, DATABASE_ROLE, SWITCHOVER_STATUS, FORCE_LOGGING, DATAGUARD_BROKER, GUARD_STATUS FROM V$DATABASE;

OPEN_MODE            DATABASE_ROLE    SWITCHOVER_STATUS    FOR DATAGUAR GUARD_S
-------------------- ---------------- -------------------- --- -------- -------
READ WRITE           PRIMARY          TO STANDBY           YES DISABLED NONE

(三)新的备库开启日志应用

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

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