Oracle误删除表数据后的数据恢复详解

Oracle误删除表数据后的恢复详解
 
测试环境:
SYSTEM:IBM AIX 5L                         Oracle Version:10gR2
 

1. undo_retention参数的查询与修改

使用show parameter undo命令查看当前的数据库参数undo_retention设置。
显示如下:
SQL> show parameter undo

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
undo_management                      string      AUTO
undo_retention                       integer     900
undo_tablespace                      string      UNDOTBS2
undo_retention(保持力),900单位是秒,即15分钟。
修改默认的undo_retention参数设置:
SQL> ALTER SYSTEM SET undo_retention=10800 SCOPE=BOTH;

System altered.

SQL> show parameter undo

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
undo_management                      string      AUTO
undo_retention                       integer     10800
undo_tablespace                      string      UNDOTBS2
undo_retention 10800,单位秒,即3小时。

2. oracle误删除表数据后的的快速恢复功能方法

2.1 方法一
通过oracle提供的回闪功能

exec dbms_flashback.enable_at_time(to_date('2011-04-15 08:21:00','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。

2.2 方法二
insert into hr.job_history
select * from hr.job_history as of timestamp to_timestamp('2011-04-15 08:20:00', 'yyyy-mm-dd hh24:mi:ss');
这种方法简单,容易掌握,功能和上面的一样,此处的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,这个限制由undo_retention 这个参数值决定。

查看FIRST_CHANGE#,NEXT_CHANGE#,FIRST_TIME
SQL> set pagesize 9999
SQL> col fscn for 999999999
SQL> col nscn for 999999999
SQL> select name,FIRST_CHANGE# fscn,NEXT_CHANGE# nscn,FIRST_TIME from v$archived_log;

当前的SCN为:
SQL> select dbms_flashback.get_system_change_number fscn from dual;
      FSCN
----------
   3435958

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
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,这一难堪的局面有所改善。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。

3. 下面我们通过一个例子来具体说明闪回查询的用法

示例
3.1 使用闪回查询前必须确定下面两个参数:
UNDO_MANAGEMENT = AUTO
undo_retention = 10800;
这个时间可以随便设,它表示在系统中保留提交了的UNDO信息的时间,10800就是保留3小时,即180分钟。
3.2 使用闪回查询

SQL> conn /as sysdba
Connected.
SQL> drop user lsf cascade;

User dropped.

SQL> create user lsf identified by lsf;

User created.

SQL> grant connect,resource to lsf;

Grant succeeded.

SQL> grant execute on dbms_flashback to lsf;

Grant succeeded.

SQL> conn lsf/lsf
Connected.
SQL> create table T(id int, name varchar2(20));

Table created.

SQL> insert into T values(1,'lsf');

1 row created.

SQL> insert into T values(2,'lsf');

1 row created.

SQL> insert into T values(3,'lsf');

1 row created.

SQL> commit;

Commit complete.

SQL> select * from T;

    ID NAME
---------- ------------------------------------------------------------
     1 lsf
     2 lsf
     3 lsf

SQL> set time on
10:12:50 SQL> delete from T where id=1;

1 row deleted.

10:13:02 SQL> commit;

Commit complete.

10:13:10 SQL> select * from T;

    ID NAME
---------- ------------------------------------------------------------
     2 lsf
     3 lsf

10:13:18 SQL> execute DBMS_FLASHBACK.ENABLE_AT_TIME(to_date('2011-04-15 10:12:50','YYYY-MM-DD HH24:MI:SS'));

PL/SQL procedure successfully completed.

10:13:50 SQL> select * from T;

    ID NAME
---------- ------------------------------------------------------------
     1 lsf
     2 lsf
     3 lsf

10:13:57 SQL> execute DBMS_FLASHBACK.DISABLE;

PL/SQL procedure successfully completed.

10:15:48 SQL> select * from T;

    ID NAME
---------- ------------------------------------------------------------
     2 lsf
     3 lsf

3.3 使用闪回查询恢复数据

10:16:59 SQL> truncate table T;

Table truncated.

10:18:15 SQL> select * from T;

no rows selected

10:18:22 SQL> insert into T values(1,'lsf');

1 row created.

10:19:42 SQL> insert into T values(2,'lsf');

1 row created.

10:19:48 SQL> insert into T values(3,'lsf');

1 row created.

10:19:55 SQL> insert into T values(4,'lsf');

1 row created.

10:20:07 SQL> insert into T values(5,'lsf');

1 row created.

10:20:15 SQL> insert into T values(6,'lsf');

1 row created.

10:20:21 SQL> commit;

Commit complete.

10:20:26 SQL> select * from T;

    ID NAME
---------- ------------------------------------------------------------
     1 lsf
     2 lsf
     3 lsf
     4 lsf
     5 lsf
     6 lsf

6 rows selected.

10:20:56 SQL> delete T;

6 rows deleted.

10:21:27 SQL> commit;

Commit complete.

10:21:40 SQL> declare
10:22:29  2 cursor flash_recover is
10:22:43  3 select * from T;
10:22:50  4 t_recode T%rowtype;
10:23:11  5 begin
10:23:14  6 DBMS_FLASHBACK.ENABLE_AT_TIME(to_date('2011-04-15 10:20:56','YYYY-MM-DD HH24:MI:SS'));
10:24:22  7 open flash_recover;
10:24:39  8 DBMS_FLASHBACK.DISABLE;
10:24:59  9 loop
10:25:05 10 FETCH flash_recover into t_recode;
10:25:24 11 EXIT WHEN flash_recover%NOTFOUND;
10:25:45 12 insert into T values(t_recode.id,t_recode.name);
10:26:35 13 end loop;
10:26:39 14 CLOSE FLASH_RECOVER;
10:26:50 15 commit;
10:26:56 16 end;
10:26:58 17 /

PL/SQL procedure successfully completed.

10:27:00 SQL> select * from T;

    ID NAME
---------- ------------------------------------------------------------
     1 lsf
     2 lsf
     3 lsf
     4 lsf
     5 lsf
     6 lsf

6 rows selected.

我们可以已经恢复了所有的6条纪录,但是由于闪回查询的局限性,有可能不能恢复所有的6条记录,原因就在下面。

4. 局限性
4.1 闪回查询是基于SCN的,虽然我们执行的是:
DBMS_FLASHBACK.ENABLE_AT_TIME(to_date('2011-04-15 10:20:56','YYYY-MM-DD HH24:MI:SS'));
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。
因此如果使用DBMS_FLASHBACK.ENABLE_AT_TIME来进行恢复,为了避免恢复失败,我们可以先等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:

10:27:27 SQL> VARIABLE SCN_SAVE NUMBER;
10:32:47 SQL> EXECUTE :SCN_SAVE := DBMS_FLASHBACK.GET_SYSTEM_CHANGE_NUMBER;

PL/SQL procedure successfully completed.

10:33:24 SQL> print SCN_SAVE;

 SCN_SAVE
----------
  3438420

10:33:41 SQL> execute DBMS_FLASHBACK.ENABLE_AT_SYSTEM_CHANGE_NUMBER(:SCN_SAVE);

PL/SQL procedure successfully completed.

10:34:31 SQL> select * from T;

    ID NAME
---------- ------------------------------------------------------------
     1 lsf
     2 lsf
     3 lsf
     4 lsf
     5 lsf
     6 lsf

6 rows selected.

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。
4.2 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。
4.3 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。
4.4 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。