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分页查询性能比较

原创 Linux操作系统 作者:alsrt 时间:2012-06-05 14:44:56 0 删除 编辑
今天做了分页查询的性能测试,发现写一个好的分页查询语句,性能查询的差别是巨大!
 
建立测试表
 
create table test as select * from dba_objects
 
执行如下分页查询语句1:
 
set autotrace on
 
select * from (select t.*, rownum rn from (select * from TEST) t where rownum < 40) where rn >21
 
执行计划如下:仅仅六个逻辑读.
 
Execution Plan
----------------------------------------------------------
Plan hash value: 891187116
----------------------------------------------------------------------------
| Id  | Operation           | Name | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------
|   0 | SELECT STATEMENT    |      |    39 |  7410 |     2   (0)| 00:00:01 |
|*  1 |  VIEW               |      |    39 |  7410 |     2   (0)| 00:00:01 |
|*  2 |   COUNT STOPKEY     |      |       |       |            |          |
|   3 |    TABLE ACCESS FULL| TEST |    39 |  3549 |     2   (0)| 00:00:01 |
----------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   1 - filter("RN">21)
   2 - filter(ROWNUM<40)

Statistics
----------------------------------------------------------
          1  recursive calls
          0  db block gets
          6  consistent gets
          0  physical reads
          0  redo size
       2158  bytes sent via SQL*Net to client
        503  bytes received via SQL*Net from client
          3  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
         18  rows processed
 
 
 
执行如下分页查询语句2:
 
SELECT * FROM
(
SELECT A.*, ROWNUM RN
FROM (SELECT * FROM TEST) A
)
WHERE RN BETWEEN 21 AND 40
 
执行计划如下:807个逻辑读.
 
Execution Plan
----------------------------------------------------------
Plan hash value: 607533624
----------------------------------------------------------------------------
| Id  | Operation           | Name | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------
|   0 | SELECT STATEMENT    |      | 59588 |    10M|   188   (7)| 00:00:03 |
|*  1 |  VIEW               |      | 59588 |    10M|   188   (7)| 00:00:03 |
|   2 |   COUNT             |      |       |       |            |          |
|   3 |    TABLE ACCESS FULL| TEST | 59588 |  5295K|   188   (7)| 00:00:03 |
----------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   1 - filter("RN"<=40 AND "RN">=21)

Statistics
----------------------------------------------------------
          1  recursive calls
          0  db block gets
        807  consistent gets
          0  physical reads
          0  redo size
       2219  bytes sent via SQL*Net to client
        503  bytes received via SQL*Net from client
          3  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
         20  rows processed
 
总结,对于一个高访问量的网站,如果采用第一种的分页查询,性能会有巨大的提升!
 
 

来自 “ ITPUB博客 ” ,链接:http://blog.itpub.net/8410760/viewspace-731957/,如需转载,请注明出处,否则将追究法律责任。

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