我们有一个中央登录,用于支持多个网站。为了存储我们用户的数据,我们有一个accounts
表,用于存储每个用户帐户,然后是每个站点的users
表,以获取站点特定信息。我们还有一个简单的connections
表,用于存储用户之间的连接。
我们注意到一个正在加入主键user_id
上的表的查询执行缓慢。我希望那里的一些SQL专家可以解释为什么它使用WHERE
来搜索users_site1表并建议我们如何优化它。这是慢查询&解释结果:
mysql> explain select a.username,a.first_name,a.last_name,a.organization_name,a.organization,a.city,a.state,a.zip,a.country,a.profile_photo,a.facebook_id,a.twitter_id,u.reviews from accounts a join users_site1 u ON a.user_id=u.user_id where a.user_id IN (select cid2 from connections where cid1=10001006 AND type="MM" AND status="A") OR a.user_id IN (select cid1 from connections where cid2=10001006 AND type="MM" AND status="A") order by RAND() LIMIT 4;
+----+--------------------+-------------+--------+-------------------+---------+---------+-----------------------+-------+----------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+--------------------+-------------+--------+-------------------+---------+---------+-----------------------+-------+----------------------------------------------+
| 1 | PRIMARY | u | ALL | PRIMARY | NULL | NULL | NULL | 79783 | Using where; Using temporary; Using filesort |
| 1 | PRIMARY | a | eq_ref | PRIMARY | PRIMARY | 4 | exampledb.u.user_id | 1 | |
| 3 | DEPENDENT SUBQUERY | connections | ref | PRIMARY,cid1,cid2 | cid2 | 6 | const,const | 2 | Using where |
| 2 | DEPENDENT SUBQUERY | connections | ref | PRIMARY,cid1,cid2 | cid1 | 6 | const,const | 1 | Using where |
+----+--------------------+-------------+--------+-------------------+---------+---------+-----------------------+-------+----------------------------------------------+
4 rows in set (0.00 sec)
以下是每个表的定义:
CREATE TABLE `accounts` (
`user_id` int(9) unsigned NOT NULL AUTO_INCREMENT,
`username` varchar(40) DEFAULT NULL,
`facebook_id` bigint(15) unsigned DEFAULT NULL,
`facebook_username` varchar(30) DEFAULT NULL,
`password` varchar(20) DEFAULT NULL,
`profile_photo` varchar(100) DEFAULT NULL,
`first_name` varchar(40) DEFAULT NULL,
`middle_name` varchar(40) DEFAULT NULL,
`last_name` varchar(40) DEFAULT NULL,
`suffix_name` char(3) DEFAULT NULL,
`organization_name` varchar(100) DEFAULT NULL,
`organization` tinyint(1) unsigned DEFAULT NULL,
`address` varchar(200) DEFAULT NULL,
`city` varchar(40) DEFAULT NULL,
`state` varchar(20) DEFAULT NULL,
`zip` varchar(10) DEFAULT NULL,
`province` varchar(40) DEFAULT NULL,
`country` int(3) DEFAULT NULL,
`latitude` decimal(11,7) DEFAULT NULL,
`longitude` decimal(12,7) DEFAULT NULL,
`phone` varchar(20) DEFAULT NULL,
`sex` char(1) DEFAULT NULL,
`birthday` date DEFAULT NULL,
`about_me` varchar(2000) DEFAULT NULL,
`activities` varchar(300) DEFAULT NULL,
`website` varchar(100) DEFAULT NULL,
`email` varchar(150) DEFAULT NULL,
`referrer` int(4) unsigned DEFAULT NULL,
`referredid` int(9) unsigned DEFAULT NULL,
`verify` int(6) DEFAULT NULL,
`status` char(1) DEFAULT 'R',
`created` datetime DEFAULT NULL,
`verified` datetime DEFAULT NULL,
`activated` datetime DEFAULT NULL,
`network` datetime DEFAULT NULL,
`deleted` datetime DEFAULT NULL,
`logins` int(6) unsigned DEFAULT '0',
`api_logins` int(6) unsigned DEFAULT '0',
`last_login` datetime DEFAULT NULL,
`last_update` datetime DEFAULT NULL,
`private` tinyint(1) unsigned DEFAULT NULL,
`ip` varchar(20) DEFAULT NULL,
PRIMARY KEY (`user_id`),
UNIQUE KEY `username` (`username`),
KEY `facebook_id` (`facebook_id`),
KEY `status` (`status`),
KEY `state` (`state`)
);
CREATE TABLE `users_site1` (
`user_id` int(9) unsigned NOT NULL,
`facebook_id` bigint(15) unsigned DEFAULT NULL,
`facebook_username` varchar(30) DEFAULT NULL,
`facebook_publish` tinyint(1) unsigned DEFAULT NULL,
`facebook_checkin` tinyint(1) unsigned DEFAULT NULL,
`facebook_offline` varchar(300) DEFAULT NULL,
`twitter_id` varchar(60) DEFAULT NULL,
`twitter_secret` varchar(50) DEFAULT NULL,
`twitter_username` varchar(20) DEFAULT NULL,
`type` char(1) DEFAULT 'M',
`referrer` int(4) unsigned DEFAULT NULL,
`referredid` int(9) unsigned DEFAULT NULL,
`session` varchar(60) DEFAULT NULL,
`api_session` varchar(60) DEFAULT NULL,
`status` char(1) DEFAULT 'R',
`created` datetime DEFAULT NULL,
`verified` datetime DEFAULT NULL,
`activated` datetime DEFAULT NULL,
`deleted` datetime DEFAULT NULL,
`logins` int(6) unsigned DEFAULT '0',
`api_logins` int(6) unsigned DEFAULT '0',
`last_login` datetime DEFAULT NULL,
`last_update` datetime DEFAULT NULL,
`ip` varchar(20) DEFAULT NULL,
PRIMARY KEY (`user_id`)
);
CREATE TABLE `connections` (
`cid1` int(9) unsigned NOT NULL DEFAULT '0',
`cid2` int(9) unsigned NOT NULL DEFAULT '0',
`cid3` int(9) unsigned NOT NULL DEFAULT '0',
`type` char(2) NOT NULL,
`status` char(1) NOT NULL,
`created` datetime DEFAULT NULL,
`updated` datetime DEFAULT NULL,
PRIMARY KEY (`cid1`,`cid2`,`type`,`cid3`),
KEY `cid1` (`cid1`,`type`),
KEY `cid2` (`cid2`,`type`)
);
答案 0 :(得分:2)
而不是WHERE a.userid IN( ... ) OR a.userid IN( ... )
你应该使用另一个联接:
select
a.username,a.first_name,a.last_name,a.organization_name,a.organization,a.city,
a.state,a.zip,a.country,a.profile_photo,a.facebook_id,a.twitter_id,u.reviews
from accounts a
join users_site1 u ON a.user_id=u.user_id
join ( select cid2 as id from connections
where cid1=10001006 AND type="MM" AND status="A"
union
select cid1 as id from connections
where cid2=10001006 AND type="MM" AND status="A" ) c
on a.user_id = c.id
order by RAND() LIMIT 4;
答案 1 :(得分:0)
您是否尝试删除order by RAND()
并再次运行?
我的结果如下:
+----+--------------------+-------------+----------------+-------------------+---------+---------+------------------+------+----------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+--------------------+-------------+----------------+-------------------+---------+---------+------------------+------+----------------------------------------------+
| 1 | PRIMARY | a | ALL | PRIMARY | NULL | NULL | NULL | 2 | Using where; Using temporary; Using filesort |
| 1 | PRIMARY | u | ALL | PRIMARY | NULL | NULL | NULL | 2 | Using where; Using join buffer |
| 3 | DEPENDENT SUBQUERY | connections | index_subquery | PRIMARY,cid1,cid2 | PRIMARY | 14 | func,const,const | 1 | Using where |
| 2 | DEPENDENT SUBQUERY | connections | ref | PRIMARY,cid1,cid2 | PRIMARY | 14 | const,func,const | 1 | Using where |
+----+--------------------+-------------+----------------+-------------------+---------+---------+------------------+------+----------------------------------------------+
答案 2 :(得分:0)
我无论如何都不是MySQL大师,但在优化高性能应用程序方面不止一次涉及,尽管我更多地关注优化过程的实现结束而不是寻找需要优化的内容。
我看到的第一件事是子查询看起来很有效,但是使用这个where子句运行第一个查询的方式:...其中a.user_id IN(选择cid2 ...)或a.user_id IN(选择cid1来自...)是我非常谦虚的表演杀手。
我首先尝试优化性能,考虑尝试加入分解,在2次甚至3次查询中拆分您的请求。代码不太漂亮,但数据库将能够更有效地工作。在一个查询中执行所有操作更好是一个神话。
这会给你带来什么?缓存将更有效,如果使用MyISam表,当查询中包含较少的表时,锁定策略更有效,并且您将减少冗余行访问。如果你可以从Using where获得你的主查询(如果你分解那将是最后一个);使用临时;使用filesort,您将获得更快的响应。
使用SHOW SESSION STATUS和FLUSH状态配置您尝试的不同选项,也可以通过在查询中添加SQL_NO_CACHE来禁用缓存以获得您尝试的不同选项的真实比较,即SELSECT SQL_NO_CACHE a.username ...等。
分析和测量结果是您能够确定性能增益的唯一方法。不幸的是,这一步往往被忽视。
祝你好运!