连接的MySQL结构帮助(大表)
我目前有两个表用于带有简单联接的select查询。第一个表包含大约600-900万行,这被用作连接。主表是从1mil到300mil行的任意位置。但是,我注意到,当我在主表上加入超过10mil的行时,select查询会从瞬间变为非常慢的3秒多,并且会增长 这是我的表结构和查询连接的MySQL结构帮助(大表),mysql,performance,join,Mysql,Performance,Join,我目前有两个表用于带有简单联接的select查询。第一个表包含大约600-900万行,这被用作连接。主表是从1mil到300mil行的任意位置。但是,我注意到,当我在主表上加入超过10mil的行时,select查询会从瞬间变为非常慢的3秒多,并且会增长 这是我的表结构和查询 CREATE TABLE IF NOT EXISTS `links` ( `link_id` int(10) unsigned NOT NULL, `domain_id` mediumint(7) unsigned
CREATE TABLE IF NOT EXISTS `links` (
`link_id` int(10) unsigned NOT NULL,
`domain_id` mediumint(7) unsigned NOT NULL,
`parent_id` int(11) unsigned DEFAULT NULL,
`hash` int(10) unsigned NOT NULL,
`url` text NOT NULL,
`type` enum('html','pdf') DEFAULT NULL,
`processed` enum('N','Y') NOT NULL DEFAULT 'N',
UNIQUE KEY `hash` (`hash`),
KEY `idx_processed` (`processed`),
KEY `domain_id` (`domain_id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 ROW_FORMAT=COMPACT;
CREATE TABLE IF NOT EXISTS `domains` (
`domain_id` mediumint(7) unsigned NOT NULL AUTO_INCREMENT,
`name` varchar(170) NOT NULL,
`blocked` enum('N','Y') NOT NULL DEFAULT 'N',
`count` mediumint(6) NOT NULL DEFAULT '0',
`mcount` mediumint(3) NOT NULL,
PRIMARY KEY (`domain_id`),
KEY `name` (`name`),
KEY `blocked` (`blocked`),
KEY `mcount` (`mcount`),
KEY `count` (`count`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=10834389 ;
查询:
(SELECT link_id, url, hash FROM links, domains WHERE links.domain_id = domains.domain_id and mcount > 1 and processed='N' limit 200)
UNION
(SELECT link_id, url, hash FROM links where processed='N' and type='html' limit 200)
解释选择:
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+--------------+------------+-------+-------------------------+--------------- +---------+---------------------------+---------+-------------+
| 1 | PRIMARY | domains | range | PRIMARY,mcount | mcount | 3 | NULL | 257673 | Using where |
| 1 | PRIMARY | links | ref | idx_processed,domain_id | domain_id | 3 | crawler.domains.domain_id | 1 | Using where |
| 2 | UNION | links | ref | idx_processed | idx_processed | 1 | const | 7090017 | Using where |
| NULL | UNION RESULT | <union1,2> | ALL | NULL | NULL | NULL | NULL | NULL | |
+----+--------------+------------+-------+-------------------------+---------------+---------+---------------------------+---------+-------------+
现在,我正在尝试一个在链接上有20个分区的分区,使用domain_id作为键
如有其他选择,将不胜感激 单个SELECT语句将替换整个UNION语句:
SELECT link_id, url, hash
FROM links, domains
WHERE links.domain_id = domains.domain_id
AND mcount > 1
AND processed='N'
AND type='html'
这可能不是您要寻找的答案,但它应该可以帮助您简化问题。当事情突然变慢时,您可能需要检查查询执行中使用的索引的大小与各种mysql缓冲区的大小。这是出现慢度的第一个查询,而不是第二个查询。我以前应该提到这一点。对不起,请描述一下您的索引,并在慢速查询中显示哪些字段来自哪个表。