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 hh24:mi: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.

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