Oracle DataGuard主備切換可以使用傳統的手動命令切換，也可以使用dgmgr切換，本文記錄手動切換。

（一）將主庫切換為物理備庫

STEP1：檢視主庫狀態

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：需要檢查SWITCHOVER_STATUS引數，如果值為"SESSION ACTIVE"或者"TO STANDBY", 則主資料庫角色可以切換為備庫角色。

STEP2：將其切換到備庫，切換後，資料庫會關閉

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

注意：如果上一步的SWITCH_STATUS引數值為"TO STANDBY"，則 WITH SESSION SHUTDOWN 可以省略。

STEP3：啟動到mount狀態

SQL> SHUTDOWN ABORT
SQL> STARTUP MOUNT

注意：11.2.0.4版本及其以上版本不需要執行"SHUTDOWN ABORT"，因為資料庫已經在STEP2命令中關閉了。

(二) 將備庫切換成主庫並啟動到open
STEP1：檢視備庫狀態

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：需要檢查SWITCH_STATUS引數，如果值為"SESSION ACTIVE"或"TO PRIMARY"，則備庫可以切換為主庫。

STEP2： 切換到主庫

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

注意：如果上一步的SWITCH_STATUS引數值為"TO PRIMARY"，則 WITH SESSION SHUTDOWN 可以省略。

STEP3： 此時資料庫為mount狀態，需開啟資料庫

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)新的備庫開啟日誌應用

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

【完】