DB_FILE_MULTIBLOCK_READ_COUNT与性能有关的参数

一、环境
Oracle 11g RAC

公司主营业务：成都网站制作、成都做网站、移动网站开发等业务。帮助企业客户真正实现互联网宣传，提高企业的竞争能力。成都创新互联是一支青春激扬、勤奋敬业、活力青春激扬、勤奋敬业、活力澎湃、和谐高效的团队。公司秉承以“开放、自由、严谨、自律”为核心的企业文化，感谢他们对我们的高要求，感谢他们从不同领域给我们带来的挑战，让我们激情的团队有机会用头脑与智慧不断的给客户带来惊喜。成都创新互联推出和平免费做网站回馈大家。

二、测试过程

SQL> show parameter db_file

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_file_multiblock_read_count        integer     128
db_file_name_convert                 string      /oracle/oradata/, +DATADG
db_files                             integer     200

SQL> set timing on
SQL> select count(*) from tt;

  COUNT(*)
----------
   5524288

Elapsed: 00:00:11.50
SQL> alter system flush buffer_cache;

System altered.

Elapsed: 00:00:00.20
SQL> alter system flush shared_pool;

System altered.

Elapsed: 00:00:00.39
SQL> alter session set db_file_multiblock_read_count=16;

Session altered.

Elapsed: 00:00:00.00
SQL> select count(*) from tt;

  COUNT(*)
----------
   5524288

Elapsed: 00:00:08.91
SQL> alter system flush buffer_cache; 

System altered.

Elapsed: 00:00:00.12

SQL> alter system flush shared_pool;

System altered.

Elapsed: 00:00:00.06
SQL> alter session set db_file_multiblock_read_count=32;

Session altered.

Elapsed: 00:00:00.00
SQL> select count(*) from tt;

  COUNT(*)
----------
   5524288

Elapsed: 00:00:07.87
SQL> alter system flush buffer_cache; 

System altered.

Elapsed: 00:00:00.14
SQL> alter system flush shared_pool;

System altered.

Elapsed: 00:00:00.06
SQL> alter session set db_file_multiblock_read_count=64;

Session altered.

Elapsed: 00:00:00.00
SQL> select count(*) from tt;

  COUNT(*)
----------
   5524288

Elapsed: 00:00:07.05
SQL> alter system flush buffer_cache;

System altered.

Elapsed: 00:00:00.15
SQL> alter system flush shared_pool;

System altered.

Elapsed: 00:00:00.06
SQL> alter session set db_file_multiblock_read_count=128;

Session altered.

Elapsed: 00:00:00.00
SQL> select count(*) from tt;

  COUNT(*)
----------
   5524288

Elapsed: 00:00:06.62
SQL> 
SQL> 

三、小结
1、对于全表扫描来说多块读，增加每次读取的块数，可以提高性能。
2、在OLTP的系统中建议此参数设置为8、16、32
3、在OLAP的系统中建议此参数设置为128最大值

网站名称：DB_FILE_MULTIBLOCK_READ_COUNT与性能有关的参数
链接地址：http://6mz.cn/article/jcggds.html