查看数据库是否是归档模式：
SQL> show parameter db_flashback;
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
db_flashback_retention_target integer 1440
SQL> archive log list;
Database log mode Archive Mode
Automatic archival Enabled
Archive destination /oradata/arch/matrixdg
Oldest online log sequence 65
Next log sequence to archive 0
Current log sequence 67
2.设置闪回参数：
SQL> show parameter db_recovery;
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
db_recovery_file_dest string /u2/oracle/fast_recovery_area
db_recovery_file_dest_size big integer 4122M
如上：db_recovery_file_dest为闪回路径，db_recovery_file_dest_size为闪回区大小。
SQL> show parameter flashback;
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
db_flashback_retention_target integer 1440
如：db_flashback_retention_target闪回保留时间
3.关闭数据库，启用闪回
SQL>shutdown immediate
SQL>startup mount
SQL>alter database flashback on;
SQL>alter database open;
4.查询闪回状态
SQL> select flashback_on from v$database;
FLASHBACK_ON
------------------
YES
