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【Flashback】Flashback Database閃回數據庫功能實踐

上一篇?/?下一篇??2012-04-07 21:16:40 / 個人分類：備份與恢復

查看( 278 )?/?評論( 2 )?/?評分(?5?/?0?) ??Flashback?Database閃回數據庫功能極大的降低了由于用戶錯誤導致的數據丟失的恢復成本。這是一種以空間換取縮短恢復時間的解決方案，這是值得的。
? 這里給出閃回數據庫的使用方法，體驗一下這種恢復操作的便利性。

1.使用Flashback Database的前提條件
1）啟用了flashback database
2）必須打開flash recovery area，若為RAC，flash recovery area必須位于共享存儲中。
3）必須處于archivelog模式，開啟FORCE LOGGIN

2.一一確認上面的前提條件是否滿足
1）驗證是否啟用了flashback database并確認FORCE LOGGIN是否開啟
SYS@ora11g> select flashback_on,force_logging from v$database;

FLASHBACK_ON?????? FOR
------------------ ---
YES??????????????? NO

若flashback_on為“NO”，修改方法見《【Flashback】啟用Flashback Database閃回數據庫功能》（http://space.itpub.net/519536/viewspace-590636）
若force_logging為“NO”，請使如下SQL語句開啟。

SYS@ora11g> alter database force logging;

Database altered.

SYS@ora11g> select flashback_on,force_logging from v$database;

FLASHBACK_ON?????? FOR
------------------ ---
YES??????????????? YES

2）驗證是否開啟flash recovery area
此步驟在啟用閃回數據庫功能時已經確認過。
SYS@ora11g> show parameter db_recovery_file

NAME??????????????????????? TYPE??????? VALUE
--------------------------- ----------- ------------------------------
db_recovery_file_dest?????? string????? /u01/app/oracle/flash_recovery
??????????????????????????????????????? _area
db_recovery_file_dest_size? big integer 3852M

3）數據庫是否處于archivelog模式
SYS@ora11g> archive log list;
Database log mode????????????? Archive Mode
Automatic archival???????????? Enabled
Archive destination??????????? USE_DB_RECOVERY_FILE_DEST
Oldest online log sequence???? 11
Next log sequence to archive?? 13
Current log sequence?????????? 13

3.確認數據庫可以前滾到的SCN和Time的方法
如果需要恢復的數據點比這個時間還要早的話，很不幸，閃回數據庫功能將無能為力。
SYS@ora11g> alter session set nls_date_format='yyyy-mm-dd hh24:mi:ss';

Session altered.

SYS@ora11g> select oldest_flashback_scn,oldest_flashback_time from v$flashback_database_log;

OLDEST_FLASHBACK_SCN OLDEST_FLASHBACK_TI
-------------------- -------------------
???????????? 1033529 2012-04-02 03:36:40

4.閃回數據庫功能閃亮登場
1）創建測試表fd_1、fd_2和fd_3
SYS@ora11g> create?table?fd_1 as select * from dba_objects;

Table created.

SYS@ora11g> create table fd_2 as select * from fd_1;

Table created.

SYS@ora11g> create table fd_3 as select * from fd_1;

Table created.

SYS@ora11g> select count(*) from fd_1;

? COUNT(*)
----------
???? 72465

SYS@ora11g> select count(*) from fd_2;

? COUNT(*)
----------
???? 72465

SYS@ora11g> select count(*) from fd_3;

? COUNT(*)
----------
???? 72465

SYS@ora11g> set time on
21:59:40 SYS@ora11g> select sysdate from dual;

SYSDATE
-------------------
2012-04-07 21:59:44

2）truncate表fd_2、drop掉表fd_3
21:59:44 SYS@ora11g> truncate table fd_2;

Table truncated.

22:00:06 SYS@ora11g> drop table fd_3;

Table dropped.

3）使用Flashback Database功能進行恢復到刪除前的時間點2012-04-07 21:59:44
22:00:17 SYS@ora11g> shutdown immediate;
Database closed.
Database dismounted.
ORACLE?instance shut down.
22:02:04 SYS@ora11g> startup mount exclusive;
ORACLE instance started.

Total System Global Area? 313860096 bytes
Fixed Size????????????????? 1336232 bytes
Variable Size???????????? 247467096 bytes
Database Buffers?????????? 58720256 bytes
Redo Buffers??????????????? 6336512 bytes
Database mounted.
22:02:52 SYS@ora11g> Flashback Database to timestamp(to_date('2012-04-07 21:59:44','yyyy-mm-dd hh24:mi:ss'));

Flashback complete.

4）閃回后修復數據庫兩種方式之一：open read only
推薦使用這樣的方法進行恢復，因為在read only方式打開之后，將需要恢復的表EXP導出，然后通過recover database將數據庫恢復到原狀態，再將缺失的數據IMP到數據庫中。這樣操作對數據庫的影響可以降低到最小，可以保證其他表沒有數據的丟失。
read only打開后查看三張表的狀態：
22:03:57 SYS@ora11g> alter database open read only;

Database altered.

22:04:33 SYS@ora11g> select count(*) from fd_1;

? COUNT(*)
----------
???? 72465

22:04:37 SYS@ora11g> select count(*) from fd_2;

? COUNT(*)
----------
???? 72465

22:04:40 SYS@ora11g> select count(*) from fd_3;

? COUNT(*)
----------
???? 72465

取消閃回結果，恢復到閃回前狀態的方法：
22:04:43 SYS@ora11g> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
22:05:09 SYS@ora11g> startup mount;
ORACLE instance started.

Total System Global Area? 313860096 bytes
Fixed Size????????????????? 1336232 bytes
Variable Size???????????? 247467096 bytes
Database Buffers?????????? 58720256 bytes
Redo Buffers??????????????? 6336512 bytes
Database mounted.
22:06:08 SYS@ora11g> recover database;
Media recovery complete.
22:06:18 SYS@ora11g> alter database open;

Database altered.

22:06:41 SYS@ora11g> select count(*) from fd_1;

? COUNT(*)
----------
???? 72465

22:06:55 SYS@ora11g> select count(*) from fd_2;

? COUNT(*)
----------
???????? 0

22:06:59 SYS@ora11g> select count(*) from fd_3;
select count(*) from fd_3
???????????????????? *
ERROR at line 1:
ORA-00942: table or view does not exist

可見，通過上面的recover后，數據庫恢復到了閃回前的狀態。

5）閃回后修復數據庫兩種方式之二：open resetlogs
通過open resetlogs方式打開數據庫后，很顯然，閃回到時間點之后的數據將全部丟失，慎用！

SYS@ora11g> alter database open resetlogs;
SYS@ora11g> select count(*) from fd_1;

? COUNT(*)
----------
???? 72465

SYS@ora11g> select count(*) from fd_2;

? COUNT(*)
----------
???? 72465

SYS@ora11g> select count(*) from fd_3;

? COUNT(*)
----------
???? 72465

5.小結
? 這里對Flashback Database閃回數據庫的語法進行總結。閃回數據庫可以在SQL*Plus環境和RMAN環境下使用。
? 基于時間戳進行閃回數據庫操作方法：
Flashback Database to timestamp(to_date('2012-04-07 21:59:44','yyyy-mm-dd hh24:mi:ss'));
Flashback Database to timestamp(sysdate-1/24);
? 基于SCN進行閃回數據庫操作方法：
Flashback Database to 1321427;

Good luck.

secooler
12.04.07

-- The End --

轉載于:https://blog.51cto.com/aixuexi/864873

超強干貨來襲 云風專訪：近40年碼齡，通宵達旦的技術人生

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