《MYSQL数据库MySQL中InnoDB的间隙锁问题》要点：
本文介绍了MYSQL数据库MySQL中InnoDB的间隙锁问题，希望对您有用。如果有疑问，可以联系我们。
在为一个客户排除死锁问题时我遇到了一个有趣的包含InnoDB间隙锁的情形.对于一个WHERE子句不匹配任何行的非插入的写操作中,我预期事务应该不会有锁,但我错了.让我们看一下这张表及示例UPDATE.
MYSQL实例
mysql> SHOW CREATE TABLE preferences \G
*************************** 1. row ***************************
Table: preferences
Create Table: CREATE TABLE `preferences` (
`numericId` int(10) unsigned NOT NULL,
`receiveNotifications` tinyint(1) DEFAULT NULL,
PRIMARY KEY (`numericId`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)
mysql> BEGIN;
Query OK, 0 rows affected (0.00 sec)
mysql> SELECT COUNT(*) FROM preferences;
+----------+
| COUNT(*) |
+----------+
| 0 |
+----------+
1 row in set (0.01 sec)
mysql> UPDATE preferences SET receiveNotifications='1' WHERE numericId = '2';
Query OK, 0 rows affected (0.01 sec)
Rows matched: 0 Changed: 0 Warnings: 0
---TRANSACTION 4A18101, ACTIVE 12 sec 2 lock struct(s), heap size 376, 1 row lock(s) MySQL thread id 3, OS thread handle 0x7ff2200cd700, query id 35 localhost msandbox Trx read view will not see trx with id >= 4A18102, sees < 4A18102 TABLE LOCK table `test`.`preferences` trx id 4A18101 lock mode IX RECORD LOCKS space id 31766 page no 3 n bits 72 index `PRIMARY` of table `test`.`preferences` trx id 4A18101 lock_mode X
这是为什么呢,Heikki在其bug申报中做了解释,这很有意义,我知道修复起来很困难,但略带厌恶地我又希望它能被差异化处理.为完成这篇文章,让我证明下上面说到的死锁情况,下面中mysql1是第一个会话,mysql2是另一个,查询的顺序如下：
MYSQL实例
mysql1> BEGIN;
Query OK, 0 rows affected (0.00 sec)
mysql1> UPDATE preferences SET receiveNotifications='1' WHERE numericId = '1';
Query OK, 0 rows affected (0.00 sec)
Rows matched: 0 Changed: 0 Warnings: 0
mysql2> BEGIN;
Query OK, 0 rows affected (0.00 sec)
mysql2> UPDATE preferences SET receiveNotifications='1' WHERE numericId = '2';
Query OK, 0 rows affected (0.00 sec)
Rows matched: 0 Changed: 0 Warnings: 0
mysql1> INSERT INTO preferences (numericId, receiveNotifications) VALUES ('1', '1'); -- This one goes into LOCK WAIT
mysql2> INSERT INTO preferences (numericId, receiveNotifications) VALUES ('2', '1');
ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction
现在你看到导致死锁是多么的容易,因此必定要避免这种情况――如果来自于事务的INSERT部分导致非插入的写操作可能不匹配任何行的话,不要这样做,使用REPLACE INTO或使用READ-COMMITTED事务隔离.
MYSQL实例
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