開啟STANDBY庫為READ WRITE

1.取消主庫傳送歸檔

SQL> alter system set log_archive_dest_state_2=defer;

2.取消備庫應用日誌

SQL> alter database recover managed standby database cancel;

3.修改相關引數

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.開啟FLASHBACK

SQL> alter database flashback on;

5.建立還原點

SQL> create restore point before_falshback guarantee flashback database;

6.啟用STANDBY DATABASE

SQL> alter database activate standby database;

7.如果DG不是最大效能，則修改為最大效能

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

8.檢視資料庫狀態

SQL> select open_mode,database_role from v$database;

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

此時，STANDBY庫已經開啟為READ WRITE

將READ WRITE狀態重新返回為STANDBY

1.將資料庫啟動至mount狀態

SQL> startup force mount;

2.閃回

SQL> flashback database to restore point before_flashback;

3.將資料庫修改為STANDBY

SQL> alter database convert to physical standby;

4.開啟資料庫

SQL> startup force mount;

5.刪除還原點（刪除還原點需要資料庫在mount狀態，不可以是OPEN READ ONLY狀態），關閉FLASHBACK

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

6.開啟資料庫並應用日誌

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

7.主庫開啟日誌傳輸

SQL> alter system set log_archive_dest_state_2=enable;

8.主庫切換歸檔，驗證備庫是否可以應用