物理STANDBY库创建还原点（打开为read write后再变回主库）

开启STANDBY库为READ WRITE

1.取消主库传送归档

SQL> alter system set log_archive_dest_state_2=defer;

2.取消备库应用日志

SQL> alter database recover managed standby database cancel;

3.修改相关参数

SQL> alter system db_recovery_file_dest='/oracle/fast_recovery_area';
SQL> alter system set db_recovery_file_dest_size=30G;
SQL> alter system set db_flashback_retention_target=1440;

4.打开FLASHBACK

SQL> alter database flashback on;

5.创建还原点

SQL> create restore point before_falshback guarantee flashback database;

6.激活STANDBY DATABASE

SQL> alter database activate standby database;

7.如果DG不是最大性能，则修改为最大性能

SQL> startup force mount;
SQL> alter database set standby database to maximize performance;
SQL> alter database open;

8.查看数据库状态

SQL> select open_mode,database_role from v$database;

OPEN_MODE            DATABASE_ROLE
-------------------- ----------------
READ WRITE           PRIMARY

此时，STANDBY库已经开启为READ WRITE

将READ WRITE状态重新返回为STANDBY

1.将数据库启动至mount状态

SQL> startup force mount;

2.闪回

SQL> flashback database to restore point before_flashback;

3.将数据库修改为STANDBY

SQL> alter database convert to physical standby;

4.打开数据库

SQL> startup force mount;

5.删除还原点（删除还原点需要数据库在mount状态，不可以是OPEN READ ONLY状态），关闭FLASHBACK

SQL> drop restore point before_flashback;
SQL> alter database flashback off;

6.打开数据库并应用日志

SQL> alter database open read only;
SQL> alter database recover managed standby database disconnect;

7.主库开启日志传输

SQL> alter system set log_archive_dest_state_2=enable;

8.主库切换归档，验证备库是否可以应用

参考：http://www.oracle.com/us/solutions/sap/wp-ora4sap-flashback11g-1-303814.pdf