在Oracle 10.2.0.4 版本的 DataGuard 環境中將 physical standby database 轉成成 primary database 角色時，發生錯誤：

SQL> alter database commit to switchover to primary;
alter database commit to switchover to primary
*
ERROR at line 1:
ORA-16139: media recovery required

alert日誌中報的錯誤資訊為：

Tue Nov  5 15:31:19 2013
alter database commit to switchover to primary
Tue Nov  5 15:31:19 2013
ALTER DATABASE SWITCHOVER TO PRIMARY (TDB1)
Tue Nov  5 15:31:19 2013
If media recovery active, switchover will wait for completion
Database not available for switchover
  End-Of-REDO archived log file has been received
  End-Of-REDO archived log file has not been recovered
  Archived log files detected beyond End-Of-REDO
  Incomplete recovery SCN:0:667169 archive SCN:0:668379
Database not available for switchover
  End-Of-REDO archived log file has been received
  End-Of-REDO archived log file has not been recovered
  Archived log files detected beyond End-Of-REDO
  Incomplete recovery SCN:0:667169 archive SCN:0:668379
Switchover: Media recovery required - standby not in limbo
ORA-16139 signalled during: alter database commit to switchover to primary...

通過上面的資訊可以看出來，archive log已經接收到了，但是還未進行恢復。 想了想後，我在切換前的幾個小時，將physical standby database 的 Redo Apply 停掉了，所以才導致 接收到的 archive log 未被進行恢復。

登陸到physical standby database，啟動Redo Apply，以應用這些從primary database接收到的archive log。

SQL> recover managed standby database disconnect from session;
Media recovery complete.

然後再switchover to primary：

SQL> alter database commit to switchover to primary;

Database altered.