单机主备：

单节点主机，备机是物理DG。

主节点彻底挂机，把 物理DG用failover设置为主机。

备机状态： SQL> select open_mode from v$database; 

OPEN_MODE

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

READ ONLY

SQL> select open_mode from v$database; 

OPEN_MODE

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

READ ONLY

SQL> select switchover_status from v$database;

SWITCHOVER_STATUS

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

NOT ALLOWED SQL> select open_mode,protection_mode,database_role,switchover_status from v$database;

OPEN_MODE      PROTECTION_MODE   DATABASE_ROLE    SWITCHOVER_STATUS

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

READ ONLY      MAXIMUM PERFORMANCE  PHYSICAL STANDBY NOT ALLOWED

开始在备机使用failover：

SQL> shutdown immediate;

Database closed.

Database dismounted.

ORACLE instance shut down.

SQL> startup mount;  

ORA-32004: obsolete or deprecated parameter(s) specified for RDBMS instance

ORACLE instance started.

Total System Global Area 2147483648 bytes

Fixed Size     3712904 bytes

Variable Size   486541432 bytes

Database Buffers 1644167168 bytes

Redo Buffers    13062144 bytes

Database mounted.

SQL> alter database recover managed standby database finish force;

Database altered.

SQL> select switchover_status from v$database;

SWITCHOVER_STATUS

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

TO PRIMARY

SQL> alter database commit to switchover to primary;

Database altered.

SQL> alter database open;

Database altered.

SQL> select open_mode,protection_mode,database_role,switchover_status from v$database;

OPEN_MODE      PROTECTION_MODE   DATABASE_ROLE    SWITCHOVER_STATUS

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

READ WRITE      MAXIMUM PERFORMANCE  PRIMARY    RESOLVABLE GAP

完成。