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HomeDatabaseMysql Tutorial关系数据库的一些性能优化技巧

关系数据库的一些性能优化技巧

Jun 07, 2016 pm 04:24 PM
weboptimizationrelationapplication developmentperformanceSkilldatabase

对于web应用开发,多数性能瓶颈均出现在数据库上,除了采用分布式架构或云处理(大公司基本上都是),更重要的是平时程序设计时要遵照一些规则,从根本上提高系统的性能,以下总结了一些常用的规则方法,仅供参考。 1、 把数据、日志、索引放到不同的I/O设备

对于web应用开发,多数性能瓶颈均出现在数据库上,除了采用分布式架构或云处理(大公司基本上都是),更重要的是平时程序设计时要遵照一些规则,从根本上提高系统的性能,以下总结了一些常用的规则方法,仅供参考。

1、 把数据、日志、索引放到不同的I/O设备上,增加读取速度。数据量(尺寸)越大,提高I/O越重要。

2、 纵向、横向分割表,减少表的尺寸,如:可以把大数据量的字段拆分表。

3、 根据查询条件,建立索引,优化索引、优化访问方式,限制结果集的数据量。注意填充因子要适当(最好是使用默认值0)。索引应该尽量小,尽量使用字节数小的列建索引,不要对有限的几个值的列建单一索引。

4、 用OR的字句可以分解成多个查询,并且通过UNION链接多个查询。它们的速度只与是否使用索引有关,如果查询需要用到联合索引,用UNION all执行的效率更高。

5、 在查询SELECT语句中用WHERE子句限制返回的行数,避免表扫描。如果返回不必要的数据,则浪费了服务器的I/O资源,加重了网络的负担,降低了性能。如果表很大,在表扫描期间将表锁住,禁止其他的联结访问表,后果很严重。

6、 注意使用DISTINCT,在没有必要时不要用,它同UNION一样会使查询变慢。

7、 在IN后面值的列表中,将出现最频繁的值放在最前面,出现最少的放在最后面,减少判断的次数。

8、 一般在GROUP BY和HAVING子句之前就能剔除多余的行,所以尽量不要用它们来做剔除行的工作,也就是说尽可能在WHERE中过滤数据。

9、 尽量将数据的处理工作放在服务器上,减少网络的开销,如使用存储过程。存储过程是编译、优化过,并且被组织到一个执行规划里,且存储在数据库中的SQL语句(存储过程是数据库服务器端的一段程序),是控制流语言的集合,速度当然快。

10、 不要在一句话里再三地使用相同的函数,浪费资源,将结果放在变量里再调用更快。

11、 针对大量只读查询操作进行优化的方法:

  1. 数据量小的数据,可以考虑不存储在数据库中,而是通过程序常量的方式解决。
  2. 需要存储在数据库中的数据,可以考虑采用物化视图(索引视图)。当DBA在视图上创建索引时,这个视图就被物化(执行)了,并且结果集被永久地保存在唯一索引中,保存方式与一个有聚簇索引的表的保存方式相同。物化视图减除了为引用视图的查询动态建立结果集的开销,优化人员可以在查询中使用视图索引,而不需要在FROM子句中直接指定视图。
  3. 数据存储时可以考虑适当的数据冗余,以减少数据库表之间的链接操作,提高查询效率。
  4. 针对数据的特点,采取特定的索引类型。例如,位图索引等。

12、 对于SQL语句书写时的一些建议:

写语句时能够确定数据库对象所有者的,尽可能把所有者带上,如:

SELECT * FROM dbo.Users

存储过程中,参数定义最好放在最前面,尽可能一次定义,如:

DECLARE @USER_ID INT
       ,@USER_NAME   VARCHAR(50)
       ,@PASSWORD VARCHAR(50)

为参数赋值时,尽可能一次赋值,如:

SELECT @USER_ID = 1001
       ,@USER_NAME = 'xiaojun.liu'

尽量少用游标。

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