在Data Guard環境中可以利用數據庫的閃回特性將備庫以讀寫模式打開，用於執行對主數據庫的某種測試工作，當測試完畢後，再將數據庫閃回到之前的狀態，作爲備份繼續提供保護服務。
1 在備庫閃回數據庫
1）取消備庫託管恢復
SQL> alter database recover managed standby database cancel;
Database altered.
2）設置備庫的閃回恢復區
SQL> show parameter db_recover
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
db_recovery_file_dest string /u01/app/oracle/fast_recovery_
area
db_recovery_file_dest_size big integer 4560M
3）啓動閃回特性
SQL> startup mount
ORACLE instance started.
Total System Global Area 1644167168 bytes
Fixed Size 2925024 bytes
Variable Size 1073745440 bytes
Database Buffers 553648128 bytes
Redo Buffers 13848576 bytes
Database mounted.
SQL> alter database flashback on;
Database altered.
SQL> select flashback_on from v$database;
FLASHBACK_ON
------------------
YES
4）創建一個保證還原點
SQL> create restore point before_opem_rw guarantee flashback database;
Restore point created.
5）將主庫向備庫傳輸日誌的目標目的地設置爲延遲狀態
SQL> show parameter log_archive_dest_2
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
log_archive_dest_2 string SERVICE=shhai LGWR ASYNC
VALID_FOR=(ONLINE_LOGFILES,P
RIMARY_ROLE)
DB_UNIQUE_NAME=orcldg
SQL> show parameter log_archive_dest_state_2
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
log_archive_dest_state_2 string ENABLE
SQL> alter system set log_archive_dest_state_2='defer';
System altered.
6）激活物理備庫，將備庫轉換爲獨立的數據庫運行
SQL> alter database activate physical standby database;
Database altered.
SQL> alter database open;
Database altered.
SQL> select database_role,open_mode,flashback_on from v$database;
DATABASE_ROLE OPEN_MODE FLASHBACK_ON
---------------- -------------------- ------------------
PRIMARY READ WRITE YES
7）在激活後的備庫執行測試等各種操作
8）測試完畢，將數據庫閃回到保證還原點
SQL> shutdown abort
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.
Total System Global Area 1644167168 bytes
Fixed Size 2925024 bytes
Variable Size 1073745440 bytes
Database Buffers 553648128 bytes
Redo Buffers 13848576 bytes
Database mounted.
SQL> flashback database to restore point before_opem_rw;
Flashback complete.
SQL> select database_role,open_mode,flashback_on from v$database;
DATABASE_ROLE OPEN_MODE FLASHBACK_ON
---------------- -------------------- ------------------
PRIMARY MOUNTED YES
此時，數據庫仍然使獨立的數據庫，只是狀態回到了還原點。
9）將數據庫轉換爲備庫
SQL> alter database convert to physical standby ;
Database altered.
SQL> select database_role,open_mode,flashback_on from v$database;
DATABASE_ROLE OPEN_MODE FLASHBACK_ON
---------------- -------------------- ------------------
PHYSICAL STANDBY MOUNTED YES
SQL> alter database open;
Database altered.
10）在主庫啓用向備庫的日誌傳輸
SQL> alter system set log_archive_dest_state_2='enable';
System altered.
11）啓動物理備庫的日誌應用
SQL> alter database recover managed standby database disconnect from session;
Database altered.
SQL> select database_role,open_mode,flashback_on from v$database;
DATABASE_ROLE OPEN_MODE FLASHBACK_ON
---------------- -------------------- ------------------
PHYSICAL STANDBY READ ONLY WITH APPLY YES
上述演示展示了創建還原點將備庫激活，以讀寫模式打開，進行一系列的測試，並利用閃回技術還原，之後再將其轉爲備庫，整個過程比較繁瑣，並且再備庫以讀寫模式打開後，實際上是作爲一個獨立的數據庫存在，但這個期間數據庫停止接收了來自主庫的重做日誌，這在一定程度上就失去了對主庫的保護，那麼有沒有一種方法，在使備庫處於讀寫狀態時，可以繼續接收重做日誌，只是不應用？
快照數據庫（Snapshot standby database）可以做到，下面將進行演示。
2 快照備用數據庫
1）取消備庫託管恢復
SQL> alter database recover managed standby database cancel;
Database altered.
2）將備庫轉換爲快照數據庫
SQL> alter database convert to snapshot standby;
Database altered.
SQL> select database_role,open_mode,flashback_on from v$database;
DATABASE_ROLE OPEN_MODE FLASHBACK_ON
---------------- -------------------- ------------------
SNAPSHOT STANDBY MOUNTED YES
3）打開數據庫
SQL> alter database open;
Database altered.
SQL> select database_role,open_mode,flashback_on from v$database;
DATABASE_ROLE OPEN_MODE FLASHBACK_ON
---------------- -------------------- ------------------
SNAPSHOT STANDBY READ WRITE YES
4）在快照數據庫執行一系列的測試等操作；
5）轉換快照數據庫爲物理備庫
SQL> shutdown abort
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.
Total System Global Area 1644167168 bytes
Fixed Size 2925024 bytes
Variable Size 1073745440 bytes
Database Buffers 553648128 bytes
Redo Buffers 13848576 bytes
Database mounted.
SQL> alter database convert to physical standby;
Database altered.
SQL> alter database open;
Database altered.
6）備庫開啓託管恢復
SQL> alter database recover managed standby database disconnect from session;
Database altered.
7）主庫修改數據
SQL> update scott.emp set comm=1000 where empno=7369;
1 row updated.
SQL> commit;
Commit complete.
SQL> select * from scott.emp where empno=7369;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- --------- ---------- ---------- ----------
7369 SMITH CLERK 7902 17-DEC-80 800 1000 20
8）備庫驗證，一致。
SQL> select * from scott.emp where empno=7369;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- --------- ---------- ---------- ----------
7369 SMITH CLERK 7902 17-DEC-80 800 1000 20