1)、SQL> show parameter undo_retention;

NAME             TYPE   VALUE

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

undo_retention           integer   900

2)、SQL> select autoextensible

  from dba_data_files

 where tablespace_name =

       (select value from v$parameter where name = 'undo_tablespace');

AUT

---

YES

3)、SQL> select retention from dba_tablespaces

where tablespace_name = 'UNDOTBS1';

RETENTION

-----------

NOGUARANTEE

4)、业务繁忙情况

1、时间点

select *

  from hr.employees as of timestamp to_timestamp('2015-05-14 12:40:12', 'YYYY-MM-DD HH24:MI:SS');

2、时间间隔

select *

  from hr.employees as of timestamp(systimestamp - interval '5' minute) where employee_id = 500;

--hour、month

3、scn

select job_id from hr.employees as of scn 944700

where employee_id = 100;

4、会话模式

1)将闪回会话定格在15分钟前：

SQL> exec dbms_flashback.enable_at_time(systimestamp - interval '15' minute);

2)不再需要“as of”，直接查询15分钟前的数据：

SQL> select * from hr.employees

3)关闭闪回会话模式：

SQL> exec dbms_flashback.disable;

注意：处于闪回会话模式时，执行dml和ddl将报错；

      SYS用户不能进入闪回会话模式。

SELECT versions_startscn,

       versions_starttime,

       versions_endscn,

       versions_endtime,

       versions_xid,

       versions_operation,

       employee_id,

       salary

  from hr.employees versions between timestamp(systimestamp - interval '30' minute) and maxvalue

 order by 2 nulls first;