使用数据库闪回功能来恢复已经删除…

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应用范围
Oracle
Server企业版，版本号：10.2.0.1到11.2.0.2.0版本。

本文适用于任何操作系统平台。

本文目的

本文将详细叙述如何通过flshback技术来恢复被错误删除的用户。

范围及应用

本文对各种经验的DBA都适用。

操作先决条件

-数据库必须为归档模式

-数据库必须开启了Flashback功能。

-所恢复的用户，删除时间必须在db_flashback_retention_target参数所指定的范围 内，且所有的闪回及归档日志必须都有效。

-用户的schema，所有的对象都不允许有NOLOGGING操作。

使用数据库闪回功能恢复被删除的用户

本测试包含以下步骤：

步骤1：确保闪回日志有效

步骤2：模拟人为错误，即删除用户(Drop User)

步骤3：使用闪回功能

步骤4：以只读模式打开数据库闪回功能

步骤5：检查用户及数据是否有效

步骤6：对删除的shema进行完全导出操作

步骤7：使用完全恢复来使其恢复到当前状态

步骤8：导入用户来解决人为错误，即删除用户(Drop
User)错误

下面今夕详细说明：

***完整的恢复被删除的用户***

1.
确保数据库处于闪回模式

SQL> select flashback_on from v$database;

FLASHBACK_ON

------------------

YES

SQL> show parameter flash

NAME VALUE

------------------------------- -----------

db_flashback_retention_target 1440

SQL> select
oldest_flashback_scn,oldest_flashback_time from
$flashback_database_log ;

OLDEST_FLASHBACK_SCN OLDEST_FLASHBACK_TIM

---------------------------------
--------------------------------

24300236 29-MAY-2009 12:56:13

2.
模拟操作，以一个用户创建表，并删除此用户。

SQL> conn falshback_test/flashback

Connected.

SQL> create table flashback_testing ( col1
varchar2(20));

Table created.

SQL> insert into flashback_testing values (
'flashback testing');
1
row created.

SQL> commit;

Commit complete.

SQL> alter session set nls_date_format='DD-MON-YYYY
HH24:MI:SS';

Session altered.

SQL> select sysdate from dual;

SYSDATE

--------------------

29-MAY-2009 14:32:50

SQL> conn / as sysdba

Connected.

SQL> drop user falshback_test CASCADE;

User dropped.

3.
为了恢复丢失的schema，使用数据库闪回特性来恢复到删除用户之前的某个时间点

SQL> shutdown immediate;

Database closed.

Database dismounted.

ORACLE instance shut
down.

SQL> startup mount;

ORACLE instance started.

Total System Global Area 289406976 bytes

Fixed Size 1290208 bytes

Variable Size 142606368 bytes

Database Buffers 142606336 bytes

Redo Buffers 2904064 bytes

Database mounted.

SQL> flashback database to timestamp
to_date('29-MAY-2009 14:30:00','DD-MON-YYYY

HH24:MI:SS');

Flashback complete.

4.
以只读模式打开数据库

SQL> alter database open read only;

Database altered.

5.
检查用户及其数据

SQL> conn FALSHBACK_TEST/flashback

Connected.

SQL> select * from flashback_testing;

COL1

--------------------

flashback testing
SQL>
exit

6.
导出用户

C:\>exp owner=falshback_test
file=E:\temp\exp1.dmp

Export: Release 10.2.0.4.0 - Production on Fri May 29 20:23:40
2009

Copyright (c) 1982, 2005, Oracle. All rights reserved.

Username: / as sysdba

Connected to: Oracle Database 10g Enterprise Edition Release
10.2.0.4.0 - Production

With the Partitioning, OLAP and Data Mining options

Export done in WE8MSWIN1252 character set and AL16UTF16 NCHAR
character set

About to export specified users ...

. exporting pre-schema procedural objects and actions

. exporting foreign function library names for user
FALSHBACK_TEST

. exporting PUBLIC type synonyms

. exporting private type synonyms

. exporting object type definitions for user FALSHBACK_TEST

About to export FALSHBACK_TEST's objects ...

. about to export FALSHBACK_TEST's tables via Conventional Path
...

. . exporting table FLASHBACK_TESTING 1 rows exported

. exporting synonyms

. exporting views

....

. exporting statistics

Export terminated successfully without warnings

7.
关闭数据库，恢复数据库到当前状态

SQL> shutdown immediate;

Database closed.

Database dismounted.

ORACLE instance shut down.

SQL> startup mount;

ORACLE instance started.

Total System Global Area 289406976 bytes

Fixed Size 1290208 bytes

Variable Size 142606368 bytes

Database Buffers 142606336 bytes

Redo Buffers 2904064 bytes

Database mounted.

SQL> recover database;

Media recovery complete.

SQL> alter database open;

Database altered.

现在，数据库已恢复到未删除用户时的状态，但我们在其删除前将其从数据库中全部导出并转储了。

8.
创建被删除的用户，且通过转储的数据导入到数据库中

SQL> create user falshback_test identified by
flashback default tablespace users quota unlimited on users;

User created.

SQL> -- Grant the necessary priviledge to that
user

C:\>imp full=y file=E:\temp\exp1.dmp

Import: Release 10.2.0.4.0 - Production on Fri May 29 20:26:14
2009

Copyright (c) 1982, 2005, Oracle. All rights reserved.

Username: / as sysdba

Connected to: Oracle Database 10g Enterprise Edition Release
10.2.0.4.0 - Production

With the Partitioning, OLAP and Data Mining options

Export file created by EXPORT:V10.02.01 via conventional path

import done in WE8MSWIN1252 character set and AL16UTF16 NCHAR
character set

. importing SYS's objects into SYS

. importing FALSHBACK_TEST's objects into FALSHBACK_TEST

. . importing table "FLASHBACK_TESTING" 1 rows imported

Import terminated successfully without warnings.

现在，数据库已经恢复了删除的表，也没有数据丢失了。

本文局限

l 如果任何闪回日志或归档日志丢失，则以上操作均无法进行

l 如果恢复这些NOLOGGING事务块之后，进行了NOLOGGING操作，将发生故障。因此，应尽量避免在一个使用了NOLOGGING操作的时间点或SCN，进行数据库闪回操作。