标签：

sql及索引优化

开启慢查询日志

查看慢查询日志是否打开

mysql> show variables like ‘slow_query_log‘;

+----------------+-------+
| Variable_name | Value |
+----------------+-------+
| slow_query_log | OFF |
+----------------+-------+
1 row in set (0.00 sec)

mysql> set global slow_query_log=on;
Query OK, 0 rows affected (0.05 sec)

慢查询日志文件存储位置

mysql> show variables like ‘%slow_query_log_file%‘;
+---------------------+----------------------------------------------+
| Variable_name | Value |
+---------------------+----------------------------------------------+
| slow_query_log_file | C:\xampp\mysql\data\80CEAE742547827-slow.log |
+---------------------+----------------------------------------------+
2 rows in set (0.00 sec)

是否记录没有使用索引的sql

mysql> show variables like ‘%log_queries_not_using%‘;
+-------------------------------+-------+
| Variable_name | Value |
+-------------------------------+-------+
| log_queries_not_using_indexes | OFF |

+-------------------------------+-------+
1 row in set (0.00 sec)

mysql> set global log_queries_not_using_indexes=on;
Query OK, 0 rows affected (0.00 sec)

执行时间大于N秒的SQL会被记录

mysql> show variables like ‘%long_query%‘;
+-----------------+-----------+
| Variable_name | Value |
+-----------------+-----------+
| long_query_time | 10.000000 |
+-----------------+-----------+
1 row in set (0.00 sec)

mysql> set global long_query_time=1;
Query OK, 0 rows affected (0.00 sec)

group by语句优化

优化前

select actor.first_name, actor.last_name, count(*)
from sakila.film_actor
INNER JOIN sakila.actor USING(actor_id)
GROUP BY film_actor.actor_id

使用join子查询的方式优化后，actor表没有在使用文件排序和临时表

优化后

select actor.first_name, actor.last_name, c.cnt
from sakila.actor
INNER JOIN (
    select actor_id, count(*) as cnt from sakila.film_actor GROUP BY actor_id
) as c using(actor_id)

虽然优化后仍然扫描了200行的记录，但是actor表没有使用文件排序和临时表

数据结构优化

系统配置优化

服务器硬件优化

mysql性能优化

标签：

原文地址：http://www.cnblogs.com/phpfans/p/4749110.html