分类： Oracle
2010-03-30 20:45:20
Flashback Database是Oracle10g的新增功能，在启动Flashback Database之后，它定期将已发生变化的块写入闪回日志的日志文件中。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 (RVWR)的新过程写入。这是Oracle10g的新增进程。
$ ps -ef|grep rvwr|grep -v grep
oracle 27231 1 0 17:10:30 ? 0:00 ora_rvwr_eygle
与常规的重做日志（redo logs）不同，回闪日志既不需要由DBA创建，也不需要由他们维护；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。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。
1.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
Oracle会在闪回区记录日志.
$ 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.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
4.进行闪回操作
SYS AS SYSDBA on 2005-03-29 17:03:43 >shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SYS AS SYSDBA on 2005-03-29 17:04:04 >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 session set nls_date_format='yyyy-mm-dd hh24:mi:ss';
Session altered.
SYS AS SYSDBA on 2005-03-29 17:05:31 >select * from V$FLASHBACK_DATABASE_LOG;
OLDEST_FLASHBACK_SCN OLDEST_FLASHBACK_TI RETENTION_TARGET FLASHBACK_SIZE ESTIMATED_FLASHBACK_SIZE
-------------------- ------------------- ---------------- -------------- ------------------------
10642627 2005-03-29 17:01:02 1440 8192000 0
SYS AS SYSDBA on 2005-03-29 17:06:38 >flashback database to timestamp
2 to_timestamp ('2005-03-29 17:02:28','yyyy-mm-dd hh24:mi:ss');
Flashback complete.
5.只读打开，验证数据
SYS AS SYSDBA on 2005-03-29 17:06:58 >alter database open read only;
Database altered.
SYS AS SYSDBA on 2005-03-29 17:07:07 >desc t3
ERROR:
ORA-04043: object t3 does not exist
SYS AS SYSDBA on 2005-03-29 17:07:39 >desc t1
ERROR:
ORA-04043: object t1 does not exist
6.继续修正恢复
SYS AS SYSDBA on 2005-03-29 17:07:42 >alter database close;
Database altered.
SYS AS SYSDBA on 2005-03-29 17:07:49 >flashback database to timestamp
2 to_timestamp ('2005-03-29 17:02:48','yyyy-mm-dd hh24:mi:ss');
Flashback complete.
SYS AS SYSDBA on 2005-03-29 17:08:17 >alter database open;
alter database open
*
ERROR at line 1:
ORA-16196: database has been previously opened and closed
SYS AS SYSDBA on 2005-03-29 17:08:24 >alter database dismount;
Database altered.
SYS AS SYSDBA on 2005-03-29 17:08:35 >shutdown
ORA-01507: database not mounted
ORACLE instance shut down.
SYS AS SYSDBA on 2005-03-29 17:08:48 >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 open read only;
Database altered.
SYS AS SYSDBA on 29-MAR-05 >select count(*) from t1;
COUNT(*)
----------
12
7.resetlogs打开数据库
SYS AS SYSDBA on 29-MAR-05 >shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SYS AS SYSDBA on 29-MAR-05 >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 open resetlogs;
Database altered.
SYS AS SYSDBA on 29-MAR-05 >
注意，一旦resetlogs之后，将不能再flashback至resetlogs之前的时间点。
