oracle误删除表数据后的恢复详解.doc

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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. 当前的SCN为: SQL> select dbms_flashback.get_system_change_number fscn from dual; FSCN -------------------- 12930142214 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. 数据恢复简单例子简介在过去，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，这一个难堪局面有所改善。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。下面我们通过一个例子来具体说明闪回查询的用法。二、示例 1、使用闪回查询前必须确定下面两个参数： UNDO_MANAGEMENT = AUTO undo_retention = 1200; #这个时间可以随便设，他表示在系统中保留提交了的UNDO信息的时间，1200就是保留20分钟。 2、使用闪回查询 SQL> conn sys/sys as sysdba Connected. SQL> create user flash identified by flash; User created. SQL> grant connect, resource to flash; Grant succeeded. SQL> grant execute on dbms_flashback to flash; Grant succeeded. SQL> conn flash/flash Connected. SQL> set echo on SQL> create table t (a varchar2(10)); Table created. SQL> insert into t values('gototop'); 1 row created. SQL> insert into t values(''); 1 row created. SQL> / SQL> select * from t; A ---------- gototop SQL> set time on 15:00:22 SQL> 15:00:22 SQL> 15:00:23 SQL> delete t where a='gototop'; 1 row deleted. 15:00:35 SQL> commit; Commit complete. 15:00:38 SQL> select * from t; A ---------- 15:08:22 SQL> execute DBMS_FLASHBACK.ENABLE_AT_TIME(to_date('2003-05-16 15:00:00')); PL/SQL procedure successfully completed. 15:09:02 SQL> select * from t; A ---------- gototop 15:16:43 SQL> execute DBMS_FLASHBACK.DISABLE; PL/SQL procedure successfully completed. 15:17:05 SQL> select * from t; A ---------- 3、使用闪回查询恢复数据： 15:36:55 SQL> select * from t; no rows selected 15:36:57 SQL> insert into t values(''); 1 row created. 15:37:15 SQL> / 1 row created. 15:37:16 SQL> / 1 row created. 15:37:17 SQL> / 1 row created. 15:37:18 SQL> / 1 row created. 15:37:19 SQL> commit; Commit complete. 15:37:21 SQL> / Commit complete. 15:37:22 SQL> / Commit complete. 15:37:23 SQL> select * from t; A ---------- 6 rows selected. 15:37:28 SQL> 15:38:44 SQL> delete t; 6 rows deleted. 15:38:50 SQL> commit; Commit complete. 15:38:53 SQL> commit; Commit complete. 15:38:54 SQL> / Commit complete. 15:38:57 SQL> declare 15:39:28 2 cursor flash_recover is 15:39:28 3 select * from t; 15:39:28 4 t_recode t%rowtype; 15:39:28 5 begin 15:39:28 6 DBMS_FLASHBACK.ENABLE_AT_TIME(to_date('2003-05-16 15:37:23')); 15:39:28 7 open FLASH_RECOVER; 15:39:28 8 DBMS_FLASHBACK.DISABLE; 15:39:28 9 loop 15:39:28 10 FETCH FLASH_RECOVER INTO t_recode; 15:39:28 11 EXIT WHEN FLASH_RECOVER%NOTFOUND; 15:39:28 12 insert into t values (t_recode.a); 15:39:28 13 end loop; 15:39:28 14 CLOSE FLASH_RECOVER; 15:39:28 15 commit; 15:39:28 16 end; 15:39:28 17 / PL/SQL procedure successfully completed. 15:39:28 SQL> 15:39:28 SQL> 15:39:31 SQL> select * from t; A ---------- 15:39:35 SQL> 我们可以已经恢复了5条纪录，但我们要恢复的6条纪录，为什么会少一条呢？原因就在下面。三、局限性 1、闪回查询是基于SCN的，虽然我执行的是： DBMS_FLASHBACK.ENABLE_AT_TIME(to_date('2003-05-16 15:37:23')); 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。这正是上面我们进行恢复时少了一条的原因。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： 15:58:58 SQL> VARIABLE SCN_SAVE NUMBER; 16:13:43 SQL> EXECUTE :SCN_SAVE := DBMS_FLASHBACK.GET_SYSTEM_CHANGE_NUMBER; PL/SQL procedure successfully completed. 16:13:50 SQL> print SCN_SAVE; SCN_SAVE ---------- 2.1202E+11 16:28:34 SQL> execute DBMS_FLASHBACK.ENABLE_AT_SYSTEM_CHANGE_NUMBER(:SCN_SAVE); PL/SQL procedure successfully completed. 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。 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。 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、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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