出处:http://www.jb51.net/article/51508.htm
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:
1、MySQL常用存储引擎的锁机制
MyISAM和MEMORY采用表级锁(table-level locking)
BDB采用页面锁(page-level locking)或表级锁,默认为页面锁
InnoDB支持行级锁(row-level locking)和表级锁,默认为行级锁
2、各种锁特点
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
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
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
3、各种锁的适用场景
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
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
4、死锁
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。
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.
5、死锁举例分析
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。
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。
例如,一个表db.tab_test,结构如下:
id:主键;
state:状态;
time:时间;
索引:idx_1 (state, time)
出现死锁日志如下:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
|
***(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:
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。
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。
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。
6、解决办法
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:
1
2
|
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!
出处:http://www.jb51.net/article/51508.htm
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:
1、MySQL常用存储引擎的锁机制
MyISAM和MEMORY采用表级锁(table-level locking)
BDB采用页面锁(page-level locking)或表级锁,默认为页面锁
InnoDB支持行级锁(row-level locking)和表级锁,默认为行级锁
2、各种锁特点
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
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
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
3、各种锁的适用场景
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
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
4、死锁
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。
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.
5、死锁举例分析
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。
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。
例如,一个表db.tab_test,结构如下:
id:主键;
state:状态;
time:时间;
索引:idx_1 (state, time)
出现死锁日志如下:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
|
***(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:
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。
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。
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。
6、解决办法
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:
1
2
|
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!