Oracle 11g引入Snapshot Standby，允许standby database以read-write模式打开。当切换回standby模式，所有在read-write模式的修改都丢失。它是通过flashback database实现，但是standby database不需要显式启用flashback database。@H_404_1@

如果使用RAC，关闭所有其他实例，而保留一个实例。确保实例在mount模式。
shutdown immediate;
startup mount;@H_404_1@

1.关闭managed recovery
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;@H_404_1@

2.转换standby为一个snapshot standby。@H_404_1@

SELECT flashback_on FROM v$database;@H_404_1@

FLASHBACK_ON
------------------
NO@H_404_1@

ALTER DATABASE CONVERT TO SNAPSHOT STANDBY;
ALTER DATABASE OPEN;
SELECT flashback_on FROM v$database;@H_404_1@

FLASHBACK_ON
------------------
RESTORE POINT ONLY@H_404_1@

完成后，你可以像任何read-write数据库一样对待standby。@H_404_1@

3.将standby转换回physical standby，丢失所有转换为snapshot standby后的修改。@H_404_1@

SHUTDOWN IMMEDIATE;
STARTUP MOUNT;
ALTER DATABASE CONVERT TO PHYSICAL STANDBY;
SHUTDOWN IMMEDIATE;
STARTUP NOMOUNT;
ALTER DATABASE MOUNT STANDBY DATABASE;
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT;
SELECT flashback_on FROM v$database;@H_404_1@

FLASHBACK_ON
------------------
NO@H_404_1@

现在，standby又回到了managed recovery，归档日志的传输也恢复了。注意，flashback database仍然没有开启。@H_404_1@