一、資料表結構

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、現象

　　當多個連線同時對一個表的資料進行更新操作，那麼速度將會越來越慢，持續一段時間後將出現資料表被鎖，從而影響到其它的查詢及更新。　　

儲存過程迴圈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

執行結果（速度非常慢）

時間: 29.876s

Procedure executed successfully
受影響的行: 0

200個數據更新操作，三個資料庫連線同時執行

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
 

執行結果（持續一段時間後速度越來越慢，出現等待鎖）　

# 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: 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儲存引擎支援行級鎖，innodb的行鎖是通過給索引項加鎖實現的，這就意味著只有通過索引條件檢索資料時，innodb才使用行鎖，否則使用表鎖。根據當前的資料更新語句（update jx_attach set complete=1,attach_size=63100 where cycore_file_id='56677142da502cd8907eb58f';），該條件欄位cycore_file_id並沒有新增索引，所以導致資料表被鎖。

四、解決辦法

為cycore_file_id新增索引

五、最終效果（30次更新操作）

時間: 0.094s

Procedure executed successfully
受影響的行: 0