《Mysql入门MySQL死锁问题分析及解决方法实例详解》要点：
本文介绍了Mysql入门MySQL死锁问题分析及解决方法实例详解，希望对您有用。如果有疑问，可以联系我们。
MySQL死锁问题是很多程序员在项目开发中常遇到的问题,现就MySQL死锁及解决方法详解如下：MYSQL实例
1、MySQL常用存储引擎的锁机制MYSQL实例
MyISAM和MEMORY采用表级锁(table-level locking)MYSQL实例
BDB采用页面锁(page-level locking)或表级锁,默认为页面锁MYSQL实例
InnoDB支持行级锁(row-level locking)和表级锁,默认为行级锁MYSQL实例
2、各种锁特点MYSQL实例
表级锁：开销小,加锁快;不会出现死锁;锁定粒度大,发生锁冲突的概率最高,并发度最低MYSQL实例
行级锁：开销大,加锁慢;会出现死锁;锁定粒度最小,发生锁冲突的概率最低,并发度也最高MYSQL实例
页面锁：开销和加锁时间界于表锁和行锁之间;会出现死锁;锁定粒度界于表锁和行锁之间,并发度一般MYSQL实例
3、各种锁的适用场景MYSQL实例
表级锁更适合于以查询为主,只有少量按索引条件更新数据的应用,如Web应用MYSQL实例
行级锁则更适合于有大量按索引条件并发更新数据,同时又有并发查询的应用,如一些在线事务处理系统MYSQL实例
4、死锁MYSQL实例
是指两个或两个以上的进程在执行过程中,因争夺资源而造成的一种互相等待的现象,若无外力作用,它们都将无法推进下去.MYSQL实例
表级锁不会产生死锁.所以解决死锁主要还是针对于最常用的InnoDB.MYSQL实例
5、死锁举例分析MYSQL实例
在MySQL中,行级锁并不是直接锁记录,而是锁索引.索引分为主键索引和非主键索引两种,如果一条sql语句操作了主键索引,MySQL就会锁定这条主键索引；如果一条语句操作了非主键索引,MySQL会先锁定该非主键索引,再锁定相关的主键索引.MYSQL实例
在UPDATE、DELETE操作时,MySQL不仅锁定WHERE条件扫描过的所有索引记录,而且会锁定相邻的键值,即所谓的next-key locking.MYSQL实例
例如,一个表db.tab_test,结构如下：MYSQL实例
id：主键；
state：状态；
time：时间；
索引：idx_1 (state, time)MYSQL实例
出现死锁日志如下：MYSQL实例
***(1) TRANSACTION: TRANSACTION 0 677833455, ACTIVE 0 sec, process no 11393, OS thread id 278546 starting index read mysql tables in use 1, locked 1 LOCK WAIT 3 lock struct(s), heap size 320 MySQL thread id 83, query id 162348740 dcnet03 dcnet Searching rows for update update tab_test set state=1064,time=now() where state=1061 and time < date_sub(now(), INTERVAL 30 minute) (任务1的sql语句) ***(1) WAITING FOR THIS LOCK TO BE GRANTED: (任务1等待的索引记录) RECORD LOCKS space id 0 page no 849384 n bits 208 index `PRIMARY` of table `db/tab_test` trx id 0 677833455 _mode X locks rec but not gap waiting Record lock, heap no 92 PHYSICAL RECORD: n_fields 11; compact format; info bits 0 0: len 8; hex 800000000097629c; asc b ;; 1: len 6; hex 00002866eaee; asc (f ;; 2: len 7; hex 00000d40040110; asc @ ;; 3: len 8; hex 80000000000050b2; asc P ;; 4: len 8; hex 800000000000502a; asc P*;; 5: len 8; hex 8000000000005426; asc T&;; 6: len 8; hex 800012412c66d29c; asc A,f ;; 7: len 23; hex 75706c6f6164666972652e636f6d2f6 8616e642e706870; asc xxx.com/;; 8: len 8; hex 800000000000042b; asc +;; 9: len 4; hex 474bfa2b; asc GK +;; 10: len 8; hex 8000000000004e24; asc N$;; *** (2) TRANSACTION: TRANSACTION 0 677833454, ACTIVE 0 sec, process no 11397, OS thread id 344086 updating or deleting, thread declared inside InnoDB 499 mysql tables in use 1, locked 1 3 lock struct(s), heap size 320, undo log entries 1 MySQL thread id 84, query id 162348739 dcnet03 dcnet Updating update tab_test set state=1067,time=now () where id in (9921180) (任务2的sql语句) *** (2) HOLDS THE LOCK(S): (任务2已获得的锁) RECORD LOCKS space id 0 page no 849384 n bits 208 index `PRIMARY` of table `db/tab_test` trx id 0 677833454 lock_mode X locks rec but not gap Record lock, heap no 92 PHYSICAL RECORD: n_fields 11; compact format; info bits 0 0: len 8; hex 800000000097629c; asc b ;; 1: len 6; hex 00002866eaee; asc (f ;; 2: len 7; hex 00000d40040110; asc @ ;; 3: len 8; hex 80000000000050b2; asc P ;; 4: len 8; hex 800000000000502a; asc P*;; 5: len 8; hex 8000000000005426; asc T&;; 6: len 8; hex 800012412c66d29c; asc A,f ;; 7: len 23; hex 75706c6f6164666972652e636f6d2f6 8616e642e706870; asc uploadfire.com/hand.php;; 8: len 8; hex 800000000000042b; asc +;; 9: len 4; hex 474bfa2b; asc GK +;; 10: len 8; hex 8000000000004e24; asc N$;; *** (2) WAITING FOR THIS LOCK TO BE GRANTED: (任务2等待的锁) RECORD LOCKS space id 0 page no 843102 n bits 600 index `idx_1` of table `db/tab_test` trx id 0 677833454 lock_mode X locks rec but not gap waiting Record lock, heap no 395 PHYSICAL RECORD: n_fields 3; compact format; info bits 0 0: len 8; hex 8000000000000425; asc %;; 1: len 8; hex 800012412c66d29c; asc A,f ;; 2: len 8; hex 800000000097629c; asc b ;; *** WE ROLL BACK TRANSACTION (1) (回滚了任务1,以解除死锁)
原因分析：MYSQL实例
当“update tab_test set state=1064,time=now() where state=1061 and time < date_sub(now(), INTERVAL 30 minute)”执行时,MySQL会使用idx_1索引,因此首先锁定相关的索引记录,因为idx_1是非主键索引,为执行该语句,MySQL还会锁定主键索引.MYSQL实例
假设“update tab_test set state=1067,time=now () where id in (9921180)”几乎同时执行时,本语句首先锁定主键索引,由于需要更新state的值,所以还需要锁定idx_1的某些索引记录.MYSQL实例
这样第一条语句锁定了idx_1的记录,等待主键索引,而第二条语句则锁定了主键索引记录,而等待idx_1的记录,这样死锁就产生了.MYSQL实例
6、解决办法MYSQL实例
拆分第一条sql,先查出符合条件的主键值,再按照主键更新记录：MYSQL实例
select id from tab_test where state=1061 and time < date_sub(now(), INTERVAL 30 minute); update tab_test state=1064,time=now() where id in(......);
至此MySQL死锁问题得以解决!MYSQL实例
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