一、数据表结构

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;

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

/*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

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）

# Time: 151208 22:41:24# User@Host: zmduan[zmduan] @  [192.168.235.1]  Id:     2# Query_time: 1.848644  Lock_time: 0.780778 Rows_sent: 0  Rows_examined: 393382SET 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