Oracle 11g开启闪回功能Flashback

Oracle的建库过程中,通常会提示是否开启闪回并指定闪回恢复区大小,我一般会选择不开启。这样,如果需要使用闪回功能,就需要手动开启。

1.环境准备
我们在Oracle11g上进行测试。

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SQL> select * from v$version;
 

BANNER

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

Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - Production

PL/SQL Release 11.2.0.3.0 - Production

CORE 11.2.0.3.0 Production

TNS for Linux: Version 11.2.0.3.0 - Production

NLSRTL Version 11.2.0.3.0 - Production

SQL>

2.查询闪回功能是否开启
可以通过查询v$database视图的flashback_on字段来获取闪回功能的状态,该字段是一个布尔类型,YES表示开启,NO表示未开启。
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SQL>
 
SQL> select flashback_on from v$database;

FLASHBACK_ON

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

NO

SQL>

3.开启归档功能 在开启闪回功能之前,我们必须首先开启数据库归档,否则数据库会报错。

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SQL>
 
SQL> archive log list;

Database log mode No Archive Mode

Automatic archival Disabled

Archive destination /u01/app/oracle/product/11.2.0/dbhome_1/dbs/arch

Oldest online log sequence 16

Current log sequence 20

SQL>

SQL> alter database flashback on;

alter database flashback on

*

ERROR at line 1:

ORA-38706: Cannot turn on FLASHBACK DATABASE logging.

ORA-38707: Media recovery is not enabled.

SQL>

ORA-38706和ORA-38707两个报错提醒我们要开启数据库归档,步骤如下;

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SQL>
 
SQL> alter database archive;

alter database archive

*

ERROR at line 1:

ORA-02231: missing or invalid option to ALTER DATABASE

SQL> alter database archivelog;

alter database archivelog

*

ERROR at line 1:

ORA-01126: database must be mounted in this instance and not open in any

instance

SQL> 
SQL>

SQL> shutdown immediate

Database closed.

Database dismounted.

ORACLE instance shut down.

SQL>

SQL> startup mount

ORACLE instance started.

Total System Global Area 941600768 bytes

Fixed Size 1348860 bytes

Variable Size 536873732 bytes

Database Buffers 398458880 bytes

Redo Buffers 4919296 bytes

Database mounted.

SQL>

SQL> alter database archivelog;

Database altered.

SQL>

SQL> alter database open;

Database altered.

SQL>

SQL> archive log list;

Database log mode Archive Mode

Automatic archival Enabled

Archive destination /u01/app/oracle/product/11.2.0/dbhome_1/dbs/arch

Oldest online log sequence 16

Next log sequence to archive 20

Current log sequence 20

SQL>

SQL>

4.开启闪回功能

4.1设置参数
闪回功能和两个初始化参数有关,我们先认识一下,其中,db_recovery_file_dest_size表示闪回恢复区大小,db_recovery_file_dest表示闪回恢复区路径。

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SQL>
 
SQL> show parameter db_recovery

NAME TYPE VALUE

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

db_recovery_file_dest string

db_recovery_file_dest_size big integer 0

SQL>
在开启闪回功能前,必须设置这两个参数,而且,二者还有先后顺序,如果顺序搞错了系统也会报错并给出提示信息。

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SQL>
 
SQL> alter system set db_recovery_file_dest=\'/home/oracle/flashback\';

alter system set db_recovery_file_dest=\'/home/oracle/flashback\'

*

ERROR at line 1:

ORA-02097: parameter cannot be modified because specified value is invalid

ORA-19802: cannot use DB_RECOVERY_FILE_DEST without DB_RECOVERY_FILE_DEST_SIZE

SQL>

SQL> alter system set db_recovery_file_dest_size=2g;

System altered.

SQL>

SQL> alter system set db_recovery_file_dest=\'/home/oracle/flashback\';

System altered.

SQL>

SQL> show parameter db_recovery

NAME TYPE VALUE

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

db_recovery_file_dest string /home/oracle/flashback

db_recovery_file_dest_size big integer 2G

SQL>

4.2开启闪回功能
需要注意的一点是,在10G中,如果要开启数据库级别的闪回,需要设置相关的参数,并且使数据库处于归档模式,然后再在MOUNT状态下开启闪回。在11G中,如果设置了相关的参数及其开启了归档,那么可以再OPEN状态下打开闪回。这也算是Oracle 11g的一个新特性。

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SQL>
 
SQL> select status from v$instance;

STATUS

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

OPEN

SQL>

SQL> alter database flashback on;

Database altered.

SQL>

SQL> select flashback_on from v$database;

FLASHBACK_ON

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

YES

SQL>
这样,我们就开启了数据库闪回功能,进而可以实现闪回数据库等功能。

5.关闭闪回功能
关闭闪回功能十分简单,一条语句就能搞定。

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SQL>
 
SQL> alter database flashback off;

Database altered.

SQL> select flashback_on from v$database;

FLASHBACK_ON

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

NO

SQL>

6.总结
从上面的过程来看,需要注意几点:

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