oracle误删除表数据后的恢复详解.doc

oracle误删除表数据后的恢复详解
一、undo_retention参数的查询、修改：
用show parameter undo;命令查看当时的数据库参数undo_retention设置。
显示如下：
undo_management                       string       AUTO
undo_retention                              integer     10800
undo_suppress_errors                  boolean      FALSE
undo_tablespace                           string       UNDOTBS1
undo_retention(保持力)，10800单位是秒。即3个小时。
修改默认的undo_retention参数设置：
ALTER SYSTEM SET undo_retention=10800 SCOPE=BOTH;
二、oracle误删除表数据后的的快速恢复功能方法：
【方法一】：
通过oracle提供的回闪功能：
exec dbms_flashback.enable_at_time(to_date('2007-07-23 10:21:00','yyyy-mm-dd hh24:mi:ss'));
set serveroutput on
DECLARE r_temp hr.job_history%ROWTYPE;
CURSOR c_temp IS SELECT * FROM hr.job_history;
BEGIN
OPEN c_temp;
dbms_flashback.disable;
LOOP
FETCH c_temp INTO r_temp;
EXIT WHEN c_temp%NOTFOUND;
insert into hr.job_history(EMPLOYEE_ID,JOB_ID,START_DATE,END_DATE) values (r_temp.EMPLOYEE_ID,r_temp.JOB_ID,r_temp.START_DATE,r_temp.END_DATE);
commit;
END LOOP;
CLOSE c_temp;
END;
这种办法可以将删除的数据恢复到对应的表中，首先要保证该用户有执行dbms_flashback包的权限
【方法二】：
insert into hr.job_history
select * from hr.job_history as of timestamp to_timestamp('2007-07-23 10:20:00', 'yyyy-mm-dd hh24mi:ss');
这种方法简单，容易掌握，功能和上面的一样时间为你误操作之前的时间，最好是离误操作比较近的，因为oracle保存在回滚保持段里的数据时间有一定的时间限制由undo_retention 这个参数值决定。
SQL> col fscn for 9999999999999999999
SQL> col nscn for 9999999999999999999
SQL> select name,FIRST_CHANGE# fscn,NEXT_CHANGE# nscn,FIRST_TIME from v$archived_log;

...................

NAME FSCN NSCN FIRST_TIME
------------------------------ -------------------- -------------------- -------------------
/mwarch/oracle/1_52413.dbf 12929941968 12929942881 2005-06-22 14:38:28
/mwarch/oracle/1_52414.dbf 12929942881 12929943706 2005-06-22 14:38:32
/mwarch/oracle/1_52415.dbf 12929943706 12929944623 2005-06-22 14:38:35
/mwarch/oracle/1_52416.dbf 12929944623 12929945392 2005-06-22 14:38:38
/mwarch/oracle/1_52417.dbf 12929945392 12929945888 2005-06-22 14:38:41
/mwarch/oracle/1_52418.dbf 12929945888 12929945965 2005-06-22 14:38:44
/mwarch/oracle/1_52419.dbf 12929945965 12929948945 2005-06-22 14:38:45
/mwarch/oracle/1_52420.dbf 12929948945 12929949904 2005-06-22 14:46:05
/mwarch/oracle/1_52421.dbf 12929949904 12929950854 2005-06-22 14:46:08
/mwarch/oracle/1_52422.dbf 12929950854 12929951751 2005-06-22 14:46:11
/mwarch/oracle/1_52423.dbf 12929951751 12929952587 2005-06-22 14:46:14
...................

/mwarch/oracle/1_52498.dbf 12930138975 12930139212 2005-06-22 15:55:57
/mwarch/oracle/1_52499.dbf 12930139212 12930139446 2005-06-22 15:55:59
/mwarch/oracle/1_52500.dbf 12930139446 12930139682 2005-06-22 15:56:00

NAME FSCN NSCN FIRST_TIME
------------------------------ -------------------- -------------------- -------------------
/mwarch/oracle/1_52501.dbf 12930139682 12930139915 2005-06-22 15:56:02
/mwarch/oracle/1_52502.dbf 12930139915 12930140149 2005-06-22 15:56:03
/mwarch/oracle/1_52503.dbf 12930140149 12930140379 2005-06-22 15:56:05
/mwarch/oracle/1_52504.dbf 12930140379 12930140610 2005-06-22 15:56:05
/mwarch/oracle/1_52505.dbf 12930140610 12930140845 2005-06-22 15:56:07

14811 rows selected.

当前的SCN为:
SQL> select dbms_flashback.get_system_change_number fscn from dual;

FSCN
--------------------
12930142214

使用应用用户尝试闪回
SQL> connect username/password
Connected.

现有数据:
SQL> select count(*) from hs_passport;

COUNT(*)
----------
851998
创建恢复表
SQL> create table hs_passport_recov as select * from hs_passport where 1=0;

Table created.

选择SCN向前恢复
SQL> select count(*) from hs_passport as of scn 12929970422;

COUNT(*)
----------
861686

尝试多个SCN，获取最佳值（如果能得知具体时间，那么可以获得准确的数据闪回）
SQL> select count(*) from hs_passport as of scn &scn;
Enter value for scn: 12929941968
old 1: select count(*) from hs_passport as of scn &scn
new 1: select count(*) from hs_passport as of scn 12929941968

COUNT(*)
----------
861684

SQL> /
Enter value for scn: 12927633776
old 1: select count(*) from hs_passport as of scn &scn
new 1: select count(*) from hs_passport as of scn 12927633776
select count(*) from hs_passport as of scn 12927633776
*
ERROR at line 1:
ORA-01466: unable to read data - table definition has changed

SQL> /
Enter value for scn: 12929928784
old 1: select count(*) from hs_passport as of scn &scn
new 1: select count(*) from hs_passport as of scn 12929928784

COUNT(*)
----------
825110

SQL> /
Enter value for scn: 12928000000
old 1: select count(*) from hs_passport as of scn &scn
new 1: select count(*) from hs_passport as of scn 12928000000
select count(*) from hs_passport as of scn 12928000000
*
ERROR at line 1:
ORA-01466: unable to read data - table definition has changed

最后选择恢复到SCN为12929941968的时间点
SQL> insert into hs_passport_recov select * from hs_passport as of scn 12929941968;

861684 rows created.

SQL> commit;

Commit complete.
数据恢复简单例子
简介

在过去，如果用户误删/更新了数据后，作为用户并没有什么直接的方法来进行恢复，他们必须求助DBA来对数据库进行恢复，到了Oracle9i，这一个难堪局面有所改善。Oracle 9i中提供了一项新的技术手段--闪回查询，用户使用闪回查询可以及时取得误操作前的数据，并可以针对错误进行相应的恢复措施，而这一切都无需DBA干预。

下面我们通过一个例子来具体说明闪回查询的用法。

二、示例

1、使用闪回查询前必须确定下面两个参数：

UNDO_MANAGEMENT = AUTO

undo_retention = 1200; #这个时间可以随便设，他表示在系统中保留提交了的UNDO信息的时间，1200就是保留20分钟。

2、使用闪回查询

SQL> conn sys/sys as sysdba

Connected.

SQL> create user flash identified by flash;

User created.

SQL> grant connect, resource to flash;

Grant succeeded.

SQL> grant execute on dbms_flashback to flash;

Grant succeeded.

SQL> conn flash/flash

Connected.

SQL> set echo on

SQL> create table t (a varchar2(10));

Table created.

SQL> insert into t values('gototop');

1 row created.

SQL> insert into t values('');

1 row created.

SQL> /

SQL> select * from t;

A

----------

gototop

SQL> set time on

15:00:22 SQL>

15:00:22 SQL>

15:00:23 SQL> delete t where a='gototop';

1 row deleted.

15:00:35 SQL> commit

Commit complete.

15:00:38 SQL> select * from t;

A

----------

15:08:22 SQL> execute DBMS_FLASHBACK.ENABLE_AT_TIME(to_date('2003-05-16 15:00:00'));

PL/SQL procedure successfully completed.

15:09:02 SQL> select * from t;

A

----------

gototop

15:16:43 SQL> execute DBMS_FLASHBACK.DISABLE;

PL/SQL procedure successfully completed.

15:17:05 SQL> select * from t;

A

----------

3、使用闪回查询恢复数据：

15:36:55 SQL> select * from t;

no rows selected

15:36:57 SQL> insert into t values('');

1 row created.

15:37:15 SQL> /

1 row created.

15:37:16 SQL> /

1 row created.

15:37:17 SQL> /

1 row created.

15:37:18 SQL> /

1 row created.

15:37:19 SQL> commit;

Commit complete.

15:37:21 SQL> /

Commit complete.

15:37:22 SQL> /

Commit complete.

15:37:23 SQL> select * from t;

A

----------

6 rows selected.

15:37:28 SQL>

15:38:44 SQL> delete t;

6 rows deleted.

15:38:50 SQL> commit;

Commit complete.

15:38:53 SQL> commit;

Commit complete.

15:38:54 SQL> /

Commit complete.

15:38:57 SQL> declare

15:39:28 2 cursor flash_recover is

15:39:28 3 select * from t;

15:39:28 4 t_recode t%rowtype;

15:39:28 5 begin

15:39:28 6 DBMS_FLASHBACK.ENABLE_AT_TIME(to_date('2003-05-16 15:37:23'));

15:39:28 7 open FLASH_RECOVER;

15:39:28 8 DBMS_FLASHBACK.DISABLE;

15:39:28 9 loop

15:39:28 10 FETCH FLASH_RECOVER INTO t_recode;

15:39:28 11 EXIT WHEN FLASH_RECOVER%NOTFOUND;

15:39:28 12 insert into t values (t_recode.a);

15:39:28 13 end loop;

15:39:28 14 CLOSE FLASH_RECOVER;

15:39:28 15 commit;

15:39:28 16 end;

15:39:28 17 /

PL/SQL procedure successfully completed.

15:39:28 SQL> 15:39:28 SQL>

15:39:31 SQL> select * from t;

A

----------

15:39:35 SQL>

我们可以已经恢复了5条纪录，但我们要恢复的6条纪录，为什么会少一条呢？原因就在下面。

三、局限性

1、闪回查询是基于SCN的，虽然我执行的是：

DBMS_FLASHBACK.ENABLE_AT_TIME(to_date('2003-05-16 15:37:23'));

但Oracle并不会精确的这个时间点，而是ROUND DOWN到最近的一次SCN，然后从这个SCN开始进行恢复。而Oracle 9i是每五分钟记录一次SCN的，并将SCN和对应时间的映射做个纪录。

这正是上面我们进行恢复时少了一条的原因。因此如果使用DBMS_FLASHBACK.ENABLE_AT_TIME来进行恢复，为了避免恢复失败，我可以先等5分钟，然后再进行恢复。

使用DBMS_FLASHBACK.ENABLE_AT_TIME进行恢复还有一个缺点，那就是在Oracle 9i中SCN和对应时间的映射信息只会保留5天，因此我们无法通过DBMS_FLASHBACK.ENABLE_AT_TIME来恢复5天前的数据。如果你想使用闪回查询来恢复5天前的数据，你必须自己来确定需要恢复的SCN，然后使用

DBMS_FLASHBACK.ENABLE_AT_SYSTEM_CHANGE_NUMBER(SCN_NUMBER); 来定位你的恢复时间点，下面是使用方法：

15:58:58 SQL> VARIABLE SCN_SAVE NUMBER;

16:13:43 SQL> EXECUTE :SCN_SAVE := DBMS_FLASHBACK.GET_SYSTEM_CHANGE_NUMBER;

PL/SQL procedure successfully completed.

16:13:50 SQL> print SCN_SAVE;

SCN_SAVE

----------

2.1202E+11

16:28:34 SQL> execute DBMS_FLASHBACK.ENABLE_AT_SYSTEM_CHANGE_NUMBER(:SCN_SAVE);

PL/SQL procedure successfully completed.

另外，在使用DBMS_FLASHBACK.ENABLE_AT_TIME前，你必须设定你的NLS_DATE_FORMAT的精确程度，Oracle默认的是精确到天，如果你不设定，像上面的例子你不会得到预期结果。

2、如果你使用sysdate和DBMS_FLASHBACK.GET_SYSTEM_CHANGE_NUMBER来获取时间点或者SCN值，你必须注意它们取得都是当前的时间点和SCN值。

3、你只能在事务开始时进入闪回查询模式，如果之前有DML操作，则必须COMMIT。

4、闪回查询无法恢复到表结构改变之前，因为闪回查询使用的当前的数据字典。