MOVE和CTAS比較(續)

發表於 2012 年 01 月 10 日 由 惜分飛

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標題：MOVE和CAST比較(續)

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本篇文章是MOVE和CAST比較的續篇，主要是對於第一篇中沒有涉及到的redo和undo的情況加以敘述
1.查詢move產生redo和undo量

SQL> alter system flush buffer_cache;

 

System altered.

 

SQL> alter system flush shared_pool;

 

System altered.

 

SQL> select a.name, b.value

  2  from v$statname a, v$mystat b 

  3  where a.statistic# = b.statistic#

  4  and lower(a.name) in

  5  ('redo size','undo change vector size'); 

 

NAME                                          VALUE

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

redo size                                       844

undo change vector size                         136

 

SQL> ALTER TABLE CHF.T_XIFENFEI_MOVE MOVE TABLESPACE TEST_OCP;

    

Table altered.

 

SQL> select a.name, b.value

  2  from v$statname a, v$mystat b 

  3  where a.statistic# = b.statistic#

  4  and lower(a.name) in

  5  ('redo size','undo change vector size');   

 

NAME                                          VALUE

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

redo size                                 873074928

undo change vector size                      110748

 

--產生redo

SQL> select 873074928-844 "redo size" from dual;

 

 redo size

----------

 873074084

 

--產生undo

SQL> select 110748-136 "undo size" from dual;

 

 undo size

----------

    110612

2.查詢cast產生redo和undo 大小

SQL> alter system flush buffer_cache;

 

System altered.

 

SQL> alter system flush shared_pool;

 

System altered.

 

SQL> select a.name, b.value

  2  from v$statname a, v$mystat b 

  3  where a.statistic# = b.statistic#

and lower(a.name) in

  4    5  ('redo size','undo change vector size');

 

NAME                                                                  VALUE

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

redo size                                                               776

undo change vector size                                                 136

 

SQL> create table chf.t_xifenfei_move_new tablespace users

  2  as

  3  select * from chf.t_xifenfei_move;

  

Table created.

 

SQL> select a.name, b.value

  2  from v$statname a, v$mystat b 

  3  where a.statistic# = b.statistic#

  4  and lower(a.name) in

  5  ('redo size','undo change vector size');

 

NAME                                                                  VALUE

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

redo size                                                         873017580

undo change vector size                                              115340

 

--產生redo

SQL> select 873017580-776 "redo size" from dual;

 

 redo size

----------

 873016804

 

--產生undo

SQL> select 115340-136 "undo size" from dual;

 

 undo size

----------

    115204

3.兩次實驗比較

--redo(分母使用cast操作產生redo)

SQL> select 873074084-873016804 "redo" from dual;

 

      redo

----------

     57280

 

SQL> select 57280/873074084 from dual;

 

57280/873074084

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

     .000065607

 

--undo(分母使用cast操作產生undo)

SQL> select 110612-115204 undo from dual;

 

         undo

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

        -4592

 

SQL> select 4592/115204 from dual;

 

4592/115204

-----------

 .039859727

通過這兩個的比較可以知道move操作產生的redo多了萬分之七不到，undo少了百分之四，這些也是在實驗允許的誤差範圍內，再說move操作還包括了cast的一些後續步驟在其中，所以通過這個驗證和上一篇試驗(MOVE和CAST比較)，基本上可以大膽操作move操作的本質就是全表掃描+append插入數據，操作過程中產生的redo大小几乎和表本身大小(872415232)相等,這個證明,move和cast都是以logging模式運行(數據庫本身是非force logging模式)

原文地址：http://www.xifenfei.com/2012/01/move%E5%92%8Ccast%E6%AF%94%E8%BE%83%E7%BB%AD.html