记一次mysql的调优_MySQL
bitsCN.com
问题现象
mysql CPU占用188%（多核）
解决方法
1.跟踪慢查询
vi /etc/my.cnf 在mysqld下增加如下内容
log-slow-queries = slow.log
long_query_time = 5
含义为记录查询时间超过5秒的SQL到slow.log
查找slow.log的内容，发现里面有大量的SQL，下面有几个SQL优化原则
a) 对where语句的字段进行建索引,假定如下SQL为slow.log的内容
select count(*) from table where table_column=‘test’
那么就要对该table_column建立索引（这只是一个普遍的规则，详细规则请到网上查）
建立了索引以后，修改一下mysql的参数
2.调整mysql参数
vi /etc/my.cnf
在[mysqld]下增加如下
tmp_table_size=1024M
增加完毕后重启mysql，再进行观察，如果还是负载很高，可以适当调高，我将这个参数调整到2048后负载就下来了
这个参数值应该根据具体情况具体对待，没有一个特定的值。
那么这个参数到底是干什么用的呢？为什么如此神奇？哈哈，当执行一个查询，如果SQL对查询进行group by 或者orderby的时候都会将结果集放在这个空间中，因此说如果这个参数很小的话，就会出现上面的问题了~~
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