确保oracle处于归档状态：

SQL> select log_mode,flashback_on from v$database;

配置参数db_recovery_file_dest、db_recovery_file_size:

SQL> alter system set db_recovery_file_dest='/home/oracle/app/oracle';
​
System altered.
​
SQL> alter system set db_recovery_file_dest_size=16g;
​
System altered.
​
SQL> show parameter db_recovery_file
​
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
db_recovery_file_dest string /home/oracle/app/oracle
db_recovery_file_dest_size big integer 16G

开启闪回：

SQL> select flashback_on from v$database;
​
FLASHBACK_ON
------------------
NO
​
SQL> alter database flashback on;
​
Database altered.
​
SQL> select flashback_on from v$database;
​
FLASHBACK_ON
------------------
YES

关闭闪回：

SQL> select flashback_on from v$database;
​
FLASHBACK_ON
------------------
YES
​
SQL> alter database flashback off;
​
Database altered.
​
​
SQL> select flashback_on from v$database;
​
FLASHBACK_ON
------------------
NO

如果是oracle 10g，开启和关闭闪回，需要将数据库至于mount状态：

shutdown immediate
startup mount
alter database flashback off;
alter database open;