Flashback Query、Flashback Table(快速闪回查询、快速闪回表)

Flashback Query闪回查询

flashback query是基于undo表空间的闪回，与之相关的参数如下：

SQL> show parameter undo

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
undo_management                string      AUTO
undo_retention                       integer     900
undo_tablespace                     string      UNDOTBS1

undo_management：undo管理方式分自动auto和手动manul两种，默认为auto。

undo_retention：此参数表示，如果undo表空间中的空间充足，那么undo数据至少为保留900秒；

undo_tablespace：指定undo表空间

注意：如果undo表空间为auto管理方式，那么当undo表空间中的空间不足的时候，还是会覆盖保留区内的undo数据，也就说这种情况下

不能保证undo数据保留900秒，900秒内不一定能恢复dml操作。特殊情况下可以用下面命令长期保留undo数据，但为影响undo空间和dml操作

SQL>alter tablespace undotbs1 retention guarantee;

示例说明：

将test01表在1分钟内删除的数据插入test01_delete表中或创建表test01_delete

SQL> insert into test01_delete select * from test01 as of timestamp systimestamp - interval '1' minute

where id not in(select id from test01);

SQL>create table test01_delete as select * from test01 as of timestamp systimestamp - interval '1' minute

where id not in(select id from test01);

--也可以基于scn闪回

Flashback Table闪回表的使用

Flashback Table和Flashback Query一样是基于undo的闪回。闪回表时用户必须拥有flashback table权限和表row movement功能;

示例：

[oracle@b1 ~]$ export NLS_DATE_FORMAT="YYYY-MM-DD HH24:MI:SS"

SQL> select to_date(sysdate,'YYYY-MM-DD HH24:MI:SS') sys_date from dual; --查看时间戳

SYS_DATE
-------------------
2013-10-06 18:11:39

SQL> select dbms_flashback.get_system_change_number from dual; --查看scn

GET_SYSTEM_CHANGE_NUMBER
------------------------
1054345

SQL> grant flashback any table to scott; --赋予scott flashback table权限

Grant succeeded.

SQL> conn scott/xyc
Connected.

SQL> select * from xyc_t1;

     EMPNO ENAME                JOB                       MGR HIREDATE                   SAL       COMM     DEPTNO
---------- -------------------- ------------------ ---------- ------------------- ---------- ---------- ----------
      7698 BLAKE                MANAGER                  7839 1981-05-01 00:00:00       2850                    30
      7902 FORD                 ANALYST                  7566 1981-12-03 00:00:00       8888                    20

SQL> delete from xyc_t1;

2 rows deleted.

SQL> commit;

Commit complete.

SQL> flashback table xyc_t1 to scn '1054345';
flashback table xyc_t1 to scn '1054345'
*
ERROR at line 1:
ORA-08189: cannot flashback the table because row movement is not enabled -‍-必须开启行移动功能

SQL> alter table xyc_t1 enable row movement; -‍-开启行移动功能

Table altered.

SQL> flashback table xyc_t1 to scn '1054345'; --基于scn闪回表

Flashback complete.

SQL> select * from xyc_t1;

SQL> flashback table xyc_t1 to timestamp to_timestamp('2013-10-06 18:10:51','YYYY-MM-DD HH24:MI:SS'); --基于时间戳闪回表

Flashback complete.

SQL> select * from xyc_t1;

SQL>