澳门贵宾会注册送豪礼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
AUTOundo_retention integer 900undo_tablespace string
UNDOTBS2undo_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
AUTOundo_retention integer 10800undo_tablespace string
UNDOTBS2undo_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 onDECLARE r_temp hr.job_history%ROWTYPE;CURSOR c_temp IS SELECT * FROM hr.job_history;BEGINOPEN c_temp;dbms_flashback.disable;LOOPFETCH 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_historyselect * 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_TIMESQL set pagesize 9999SQL
col fscn for 999999999SQL col nscn for 999999999SQL 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/passwordConnected.

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

SQL select count(*) from hs_passport as of scn Enter value for scn: 12929941968old 1: select count(*) from hs_passport as of scn &scnnew 1: select count(*) from hs_passport as of scn 12929941968 COUNT(*)---------- 861684SQL /Enter value for scn: 12927633776old 1: select count(*) from hs_passport as of scn &scnnew 1: select count(*) from hs_passport as of scn 12927633776select count(*) from hs_passport as of scn 12927633776 *ERROR at line 1:ORA-01466: unable to read data - table definition has changedSQL /Enter value for scn: 12929928784old 1: select count(*) from hs_passport as of scn &scnnew 1: select count(*) from hs_passport as of scn 12929928784 COUNT(*)---------- 825110SQL /Enter value for scn: 12928000000old 1: select count(*) from hs_passport as of scn &scnnew 1: select count(*) from hs_passport as of scn 12928000000select 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 =
AUTOundo_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 sysdbaConnected.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/lsfConnected.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 lsfSQL set time on10:12:50 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 lsf10:13:18 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 lsf10:13:57 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 selected10:18:22 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 lsf6 rows selected.10:20:56 SQL delete T;6 rows deleted.10:21:27 SQL commit;Commit complete.10:21:40 SQL declare10:22:29 2 cursor flash_recover is10:22:43 3 select * from T;10:22:50 4 t_recode T%rowtype;10:23:11 5 begin10:23:14 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 loop10:25:05 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 lsf6 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---------- 343842010:33:41 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 lsf6 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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