Home Database Mysql Tutorial MySQL数据库优化经验详谈(服务器普通配置)第1/3页

MySQL数据库优化经验详谈(服务器普通配置)第1/3页

Jun 07, 2016 pm 06:03 PM
mysql Optimization experience

同时在线访问量继续增大 对于1G内存的服务器明显感觉到吃力严重时甚至每天都会死机 或者时不时的服务器卡一下 这个问题曾经困扰了我半个多月MySQL使用是很具伸缩性的算法,因此你通常能用很少的内存运行或给MySQL更多的被存以得到更好的性能。

安装好mysql后,配制文件应该在/usr/local/mysql/share/mysql目录中,配制文件有几个,有my- huge.cnf my-medium.cnf my-large.cnf my-small.cnf,不同的流量的网站和不同配制的服务器环境,当然需要有不同的配制文件了。

一般的情况下,my-medium.cnf这个配制文件就能满足我们的大多需要;一般我们会把配置文件拷贝到/etc/my.cnf 只需要修改这个配置文件就可以了,使用mysqladmin variables extended-status –u root –p 可以看到目前的参数,有3个配置参数是最重要的,即:

key_buffer_size只对MyISAM表起作用。

key_buffer_size指定索引缓冲区的大小,它决定索引处理的速度,尤其是索引读的速度。一般我们设为16M,实际上稍微大一点的站点 这个数字是远远不够的,通过检查状态值Key_read_requests和Key_reads,可以知道key_buffer_size设置是否合理。比例key_reads / key_read_requests应该尽可能的低,至少是1:100,1:1000更好(上述状态值可以使用SHOW STATUS LIKE ‘key_read%'获得)。 或者如果你装了phpmyadmin 可以通过服务器运行状态看到,笔者推荐用phpmyadmin管理mysql,以下的状态值都是本人通过phpmyadmin获得的实例分析:

这个服务器已经运行了20天

比例接近1:8000 健康状况非常好

另外一个估计key_buffer_size的办法:把你网站数据库的每个表的索引所占空间大小加起来看看以此服务器为例:比较大的几个表索引加起来大概125M 这个数字会随着表变大而变大。

从4.0.1开始,MySQL提供了查询缓冲机制。使用查询缓冲,MySQL将SELECT语句和查询结果存放在缓冲区中,今后对于同样的SELECT语句(区分大小写),将直接从缓冲区中读取结果。根据MySQL用户手册,使用查询缓冲最多可以达到238%的效率。

通过调节以下几个参数可以知道query_cache_size设置得是否合理

Qcache_lowmem_prunes的值非常大,则表明经常出现缓冲不够的情况,同时Qcache_hits的值非常大,则表明查询缓冲使用非常频繁,此时需要增加缓冲大小Qcache_hits的值不大,则表明你的查询重复率很低,这种情况下使用查询缓冲反而会影响效率,那么可以考虑不用查询缓冲。此外,在SELECT语句中加入SQL_NO_CACHE可以明确表示不使用查询缓冲。

Qcache_free_blocks,如果该值非常大,则表明缓冲区中碎片很多query_cache_type指定是否使用查询缓冲

我设置:

得到如下状态值:

如果内存允许32M应该要往上加点

table_cache指定表高速缓存的大小。每当MySQL访问一个表时,如果在表缓冲区中还有空间,该表就被打开并放入其中,这样可以更快地访问表内容。通过检查峰值时间的状态值Open_tables和Opened_tables,可以决定是否需要增加table_cache的值。如果你发现open_tables等于table_cache,并且opened_tables在不断增长,那么你就需要增加table_cache的值了(上述状态值可以使用SHOW STATUS LIKE ‘Open%tables'获得)。注意,不能盲目地把table_cache设置成很大的值。如果设置得太高,可能会造成文件描述符不足,从而造成性能不稳定或者连接失败。

对于有1G内存的机器,推荐值是128-256。

笔者设置table_cache = 256

得到以下状态:

虽然open_tables已经等于table_cache,但是相对于服务器运行时间来说,已经运行了20天,opened_tables的值也非常低。因此,增加table_cache的值应该用处不大。如果运行了6个小时就出现上述值 那就要考虑增大table_cache。

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