SQL> select flashback_on from v$database;

FLASHBACK_ON
------------------
YES

SQL> shutdown immediate;
SQL> startup mount;
SQL> alter database archivelog;
SQL> alter database flashback on/off;　　开启关闭闪回功能
SQL> alter database open;

SQL> alter system set db_recovery_file_dest_size=80g scope=spfile;
设置闪回区位置：
SQL> alter system set db_recovery_file_dest=‘/workdb/account_flashback_area‘ scope=spfile;
设置闪回目标为5天，以分钟为单位，每天为1440分钟：
SQL> alter system set db_flashback_retention_target=7200 scope=spfile;