MySQL凭借着出色的性能、低廉的成本、丰富的资源，已经成为绝大多数互联网公司的首选关系型数据库。虽然性能出色，但所谓“好马配好鞍”，如何能够更好的使用它，已经成为开发工程师的必修课，我们经常会从职位描述上看到诸如“精通MySQL”、“SQL语句优化”、“了解数据库原理”等要求。我们知道一般的应用系统，读写比例在10:1左右，而且插入操作和一般的更新操作很少出现性能问题，遇到最多的，也是最容易出问题的，还是一些复杂的查询操作，所以查询语句的优化显然是重中之重。
问题：cpu负载过高，达到36。
现象：通过mysqladmin -uroot -p processlist 查看到大量如下信息：
Sending data select * from `rep_corp_vehicle_online_count` where corp_id = 48 and vehicle_id = 10017543
根据以上的可能是表rep_corp_vehicle_online_count的问题 做出如下测试：
查看表结构：
mysql> desc rep_corp_vehicle_online_count; +-------------+-------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-------------+-------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | corp_id | int(11) | NO | | NULL | | | vehicle_id | int(11) | NO | | NULL | | | online_day | varchar(20) | NO | | NULL | | | loc_total | int(11) | NO | | NULL | | | create_time | datetime | NO | | NULL | | | update_time | datetime | NO | | NULL | | +-------------+-------------+------+-----+---------+----------------+ 7 rows in set (0.00 sec)
查看索引，只有主键索引：
mysql> show index from rep_corp_vehicle_online_count; +-------------------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | +-------------------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ | rep_corp_vehicle_online_count | 0 | PRIMARY | 1 | id | A | 1247259 | NULL | NULL | | BTREE | | | +-------------------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 1 row in set (0.00 sec)
代码执行情况：
mysql>explain select * from rep_corp_vehicle_online_count where corp_id = 79 and vehicle_id = 10016911 and online_day = '2016-03-29'\G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: rep_corp_vehicle_online_count type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 1248495 Extra: Using where 1 row in set (0.00 sec)
表数据分析情况，重复数据很多：
mysql> select count(distinct corp_id) from rep_corp_vehicle_online_count; +-------------------------+ | count(distinct corp_id) | +-------------------------+ | 18 | +-------------------------+ 1 row in set (0.63 sec) mysql> select count(corp_id) from rep_corp_vehicle_online_count; +----------------+ | count(corp_id) | +----------------+ | 1239573 | +----------------+ 1 row in set (0.00 sec) mysql> select count(distinct vehicle_id) from rep_corp_vehicle_online_count; +----------------------------+ | count(distinct vehicle_id) | +----------------------------+ | 2580 | +----------------------------+ 1 row in set (1.03 sec) mysql>explain select count(vehicle_id) from rep_corp_vehicle_online_count; +-------------------+ | count(vehicle_id) | +-------------------+ | 1239911 | +-------------------+ 1 row in set (0.00 sec)
最后处理，创建索引：
mysql> create index r_c_v on rep_corp_vehicle_online_count(corp_id,vehicle_id); Query OK, 1487993 rows affected (6.09 sec) Records: 1487993 Duplicates: 0 Warnings: 0 mysql> show index from rep_corp_vehicle_online_count; +-------------------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | +-------------------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ | rep_corp_vehicle_online_count | 0 | PRIMARY | 1 | id | A | 1490176 | NULL | NULL | | BTREE | | | | rep_corp_vehicle_online_count | 1 | r_c_v | 1 | corp_id | A | 18 | NULL | NULL | | BTREE | | | | rep_corp_vehicle_online_count | 1 | r_c_v | 2 | vehicle_id | A | 2596 | NULL | NULL | | BTREE | | | +-------------------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 3 rows in set (0.00 sec)
添加索引过后负载降低到了1.73：
以上内容是小编给大家介绍的Mysql数据库之索引优化 ，希望对大家学习有所帮助！
