1.环境准备
我们在Oracle11g上进行测试。
点击(此处)折叠或打开
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。
点击(此处)折叠或打开
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。
点击(此处)折叠或打开
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；
点击(此处)折叠或打开
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。
点击(此处)折叠或打开
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。
点击(此处)折叠或打开
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。
点击(此处)折叠或打开
SQL>
?
SQL> select sta