巧用Flashback database功能恢复用户错误（1）

Oracle10g中有一个新增得功能Flashback Database，当你启动它以后，它会定期将已发生变化的块写入到闪回日志的日志文件中。请注意这些日志不是由传统的Log Writer (LGWR) 过程写入，而是由一种称作Recovery Writer的新过程来写入。

$ ps -ef|grep rvwr|grep -v grep
oracle 27231     1  0 17:10:30 ?        0:00 ora_rvwr_eygle

注释：与常规的重做日志有所不同，回闪日志既不需要DBA创建，也不需要DBA来维护；它们由Oracle Managed Files（OMF）自动在闪回恢复区域所指定的目录中创建。请注意这些文件不会归档，所以，如果在该目录发生介质故障后就不可能再进行恢复了。

（1）首先启用闪回数据库特性

SYS AS SYSDBA on 2005-03-29 16:42:19 >startup mount;
ORACLE instance started.
Total System Global Area  314572800 bytes
Fixed Size                  1301704 bytes
Variable Size             261890872 bytes
Database Buffers           50331648 bytes
Redo Buffers                1048576 bytes
Database mounted.
SYS AS SYSDBA on 29-MAR-05 >alter database archivelog;
Database altered.
SYS AS SYSDBA on 29-MAR-05 >alter database flashback on;
Database altered.
SYS AS SYSDBA on 29-MAR-05 >alter database open;
Database altered.
SYS AS SYSDBA on 29-MAR-05 >alter session set nls_date_format='yyyy-mm-dd hh24:mi:ss';
Session altered.
SYS AS SYSDBA on 2005-03-29 17:01:42 >SELECT OLDEST_FLASHBACK_SCN, OLDEST_FLASHBACK_TIME
  2  FROM V$FLASHBACK_DATABASE_LOG;
OLDEST_FLASHBACK_SCN OLDEST_FLASHBACK_TI
-------------------- -------------------
            10642627 2005-03-29 17:01:02

(2)闪回日志

注释：Oracle会在闪回区来记录日志。

$ pwd
/data5/flash_recovery_area/EYGLE/flashback
$ ls -l
total 32064
-rw-r-----   1 oracle   dba      8200192 Mar 29 16:49 o1_mf_14l5bclp_.flb
-rw-r-----   1 oracle   dba      8200192 Mar 29 17:31 o1_mf_14l6w5h4_.flb

(3)然后模拟用户错误

SYS AS SYSDBA on 2005-03-29 17:01:44 >archive log list;
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            USE_DB_RECOVERY_FILE_DEST
Oldest online log sequence     0
Next log sequence to archive   1
Current log sequence           1
SYS AS SYSDBA on 2005-03-29 17:01:55 >select sysdate from dual;
SYSDATE
-------------------
2005-03-29 17:02:09
SYS AS SYSDBA on 2005-03-29 17:02:16 >drop table t3;
Table dropped.
SYS AS SYSDBA on 2005-03-29 17:02:22 >select sysdate from dual;
SYSDATE
-------------------
2005-03-29 17:02:28
SYS AS SYSDBA on 2005-03-29 17:02:28 >create table t1 as select * from dba_users;
Table created.
SYS AS SYSDBA on 2005-03-29 17:02:42 >select sysdate from dual;
SYSDATE
-------------------
2005-03-29 17:02:48
SYS AS SYSDBA on 2005-03-29 17:02:48 >create table t2 as select * from dba_tablespaces;
Table created.
SYS AS SYSDBA on 2005-03-29 17:03:01 >select sysdate from dual;
SYSDATE
-------------------
2005-03-29 17:03:06
SYS AS SYSDBA on 2005-03-29 17:03:06 >select sysdate from dual;
SYSDATE
-------------------
2005-03-29 17:03:17