以下参考oracle 官方文档：

The COMPATIBLE database initialization parameter must be set to 11.0 or higher to use
the real-time query feature of the Active Data Guard option.
A physical standby database instance cannot be opened if Redo Apply is active on a
mounted instance of that database. Use the following SQL statements to stop Redo
Apply, open a standby instance read-only, and restart Redo Apply:
SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;
SQL> ALTER DATABASE OPEN;
SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE USING CURRENT LOGFILE DISCONNECT;


以下参考：http://hi.baidu.com/lichangzai/blog/item/bfee39543c154f4d574e0029.html

1. 打开物理DG时查询功能(active dataguard)。

SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;

SQL> ALTER DATABASE OPEN;

SQL> select open_mode from v$database;

OPEN_MODE

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

READ ONLY

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

SQL> select open_mode from v$database;

OPEN_MODE

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

READ ONLY WITH APPLY

也就是说，在正常启动 physical standby database后，需要再执行几个语句，才能将physical standby database 变为active dataguard状态