Oracle误删除表数据后的恢复具体解释

測试环境：

SYSTEM:IBM AIX 5L Oracle Version:10gR2

1. undo_retention參数的查询与改动

使用show parameter undo命令查看当前的数据库參数undo_retention设置。

显演示样例如以下：

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。

改动默认的undo_retention參数设置：

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高速恢复功能方法

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;
这样的办法能够将删除的数据恢复到相应的表中，首先要保证该用户有运行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');
这样的方法简单，easy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，最好是离误操作比較近的，由于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 这个參数值决定。

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（假设能得知详细时间，那么能够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.

数据恢复简单样例

在过去，假设用户误删/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，用户使用闪回查询能够及时取得误操作前的数据，并能够针对错误进行对应的恢复措施，而这一切都无需DBA干预。

3. 以下我们通过一个样例来详细说明闪回查询的使用方法

演示样例
3.1 使用闪回查询前必须确定以下两个參数：
UNDO_MANAGEMENT = AUTO
undo_retention = 10800;

这个时间能够随便设，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.

我们能够已经恢复了全部的6条纪录，可是因为闪回查询的局限性，有可能不能恢复全部的6条记录，原因就在以下。

4. 局限性

4.1 闪回查询是基于SCN的，尽管我们运行的是：
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到近期的一次SCN，然后从这个SCN開始进行恢复。而Oracle 9i是每五分钟记录一次SCN的，并将SCN和相应时间的映射做个纪录。

因此假设使用DBMS_FLASHBACK.ENABLE_AT_TIME来进行恢复，为了避免恢复失败，我们能够先等5分钟，然后再进行恢复。
使用DBMS_FLASHBACK.ENABLE_AT_TIME进行恢复另一个缺点，那就是在Oracle 9i中SCN和相应时间的映射信息仅仅会保留5天，因此我们无法通过DBMS_FLASHBACK.ENABLE_AT_TIME来恢复5天前的数据。假设你想使用闪回查询来恢复5天前的数据，你必须自己来确定须要恢复的SCN，然后使用DBMS_FLASHBACK.ENABLE_AT_SYSTEM_CHANGE_NUMBER(SCN_NUMBER); 来定位你的恢复时间点，以下是用法：
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，假设你不设定，像上面的样例你不会得到预期结果。

4.2 假设你使用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 你仅仅能在事务開始时进入闪回查询模式，假设之前有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，由于闪回查询使用的当前的数据字典。