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Oracle误删除表数据后的数据恢复详解
Oracle误删除表数据后的数据恢复详解
发布时间:2016-12-28 来源:查字典编辑
摘要:Oracle误删除表数据后的恢复详解测试环境:SYSTEM:IBMAIX5LOracleVersion:10gR21.undo_retent...

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。

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