开启闪回以及闪回的四种原理

1、首先确认db_recovery_file_dest和db_recovery_file_dest_size 有值。

sys@TEST0910> show parameter recovery

 

NAME                                 TYPE        VALUE

------------------------------------ ----------- ------------------------------

db_recovery_file_dest                string      /u01/app/oracle/fast_recovery_ area

db_recovery_file_dest_size           big integer 4122M

db_recovery_file_dest 放闪回日志，默认路径/u01/app/oracle/fast_recovery_ area

db_recovery_file_dest_size 存放闪回日志空间的大小，默认4122M

 

2、开启闪回

sys@TEST0910> shutdown immediate

Database closed.

Database dismounted.

ORACLE instance shut down.

sys@TEST0910> startup mount

ORACLE instance started.

 

Total System Global Area 2505338880 bytes

Fixed Size                  2230952 bytes

Variable Size             587203928 bytes

Database Buffers         1895825408 bytes

Redo Buffers               20078592 bytes

Database mounted.

sys@TEST0910> alter database flashback on;

 

Database altered.

 

sys@TEST0910> alter database open;

 

Database altered.

 

3、查询确认是否开启闪回

sys@TEST0910> select name,flashback_on from v$database;

 

NAME                                               FLASHBACK_ON

-------------------------------------------------- ------------------

TEST0910                                           YES

 

闪回四种不同原理

 

• flashback drop：利用recyelebin 回收站原理
• flashback table TEST10 to before drop [rename to test11];可以重命名

 

• flashback query ，依赖undo数据，先查询，在做insert
• insert into test10 select * from test10 as of timestamp to_timestamp('2013-09-23 11:52:06','yyyy-mm-dd hh24:mi:ss');

 

• flashback table 依赖undo块
• flashback table scott.test10 to scn 1952615
• insert into test10 select * from scott.test10 as of scn 1952615;

        

• flashback database DDL语句，依赖闪回区的闪回日志
• flashback database to timestamp to_timestamp('2013-09-23 15:09:52','yyyy-mm-dd hh24:mi:ss');时间减一秒。

 

• 闪回归档--create as