一、数据表结构
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CREATE TABLE `jx_attach` (
`attach_id` int(11) NOT NULL AUTO_INCREMENT,
`feed_id` int(11) DEFAULT NULL ,
`attach_name` varchar(255) NOT NULL,
`cycore_file_id` varchar(255) DEFAULT NULL ,
`attach_size` bigint(20) NOT NULL DEFAULT '0',
`complete` smallint(6) NOT NULL DEFAULT '0' ,
PRIMARY KEY (`attach_id`),
KEY `jx_trend_attach_FK` (`feed_id`) USING BTREE
) ENGINE=InnoDB AUTO_INCREMENT=394160 DEFAULT CHARSET=utf8;
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二、现象
当多个连接同时对一个表的数据进行更新操作，那么速度将会越来越慢，持续一段时间后将出现数据表被锁，从而影响到其它的查询及更新。
存储过程循环30次更新操作
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/*30次更新操作*/BEGIN DECLARE v1 INT DEFAULT 30;
WHILE v1 > 0 DO
update jx_attach set complete=1,attach_size=63100 where cycore_file_id='56677142da502cd8907eb58f';
SET v1 = v1 - 1;
END WHILE;
END |
执行结果（速度非常慢）
时间: 29.876s
Procedure executed successfully
受影响的行: 0
200个数据更新操作，三个数据库连接同时执行
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update jx_attach set complete=1,attach_size=63100 where cycore_file_id='56677142da502cd8907eb58f';
update jx_attach set complete=1,attach_size=63100 where cycore_file_id='56677142da502cd8907eb58f';
update jx_attach set complete=1,attach_size=63100 where cycore_file_id='56677142da502cd8907eb58f';
update jx_attach set complete=1,attach_size=63100 where cycore_file_id='56677142da502cd8907eb58f';
update jx_attach set complete=1,attach_size=63100 where cycore_file_id='56677142da502cd8907eb58f';
update jx_attach set complete=1,attach_size=63100 where cycore_file_id='56677142da502cd8907eb58f';
...等等 |
执行结果（持续一段时间后速度越来越慢，出现等待锁）
# User@Host: zmduan[zmduan] @ [192.168.235.1] Id: 2
# Query_time: 1.848644 Lock_time: 0.780778 Rows_sent: 0 Rows_examined: 393382
SET timestamp=1449643284;
update jx_attach set complete=1,attach_size=63100 where cycore_file_id='56677142da502cd8907eb58f';
.........
........ # User@Host: zmduan[zmduan] @ [192.168.235.1] Id: 2
# Query_time: 2.868598 Lock_time: 1.558542 Rows_sent: 0 Rows_examined: 393382
SET timestamp=1449643805;
update jx_attach set complete=1,attach_size=63100 where cycore_file_id='56677142da502cd8907eb58f';
[root@localhost log]# tail -f slow_query.log
# User@Host: zmduan[zmduan] @ [192.168.235.1] Id: 19
# Query_time: 1.356797 Lock_time: 0.000169 Rows_sent: 1 Rows_examined: 393383
SET timestamp=1449643805;
SELECT *
FROM jx_attach ja,jx_feed jf
where ja.feed_id=jf.feed_id and ja.cycore_file_id='56677146da502cd8907eb5b7';
# User@Host: zmduan[zmduan] @ [192.168.235.1] Id: 2
# Query_time: 2.868598 Lock_time: 1.558542 Rows_sent: 0 Rows_examined: 393382
SET timestamp=1449643805;
update jx_attach set complete=1,attach_size=63100 where cycore_file_id='56677142da502cd8907eb58f';
三、原因分析
MySQL的innodb存储引擎支持行级锁，innodb的行锁是通过给索引项加锁实现的，这就意味着只有通过索引条件检索数据时，innodb才使用行锁，否则使用表锁。根据当前的数据更新语句（update jx_attach set complete=1,attach_size=63100 where cycore_file_id='56677142da502cd8907eb58f';），该条件字段cycore_file_id并没有添加索引，所以导致数据表被锁。
四、解决办法
为cycore_file_id添加索引
五、最终效果（30次更新操作）
时间: 0.094s
Procedure executed successfully
受影响的行: 0