通过InnoDB监控状态分析锁占用

一、表结构

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CREATE TABLE `t` (
`id` int(11) NOT NULL,
`stage` int(11) NOT NULL,
PRIMARY KEY (`id`),
KEY `idx_b` (`stage`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8

二、表数据

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+------+---------+
| id | stage |
|------+---------|
| 1 | 1 |
| 4 | 4 |
| 9 | 9 |
| 15 | 15 |
+------+---------+

三、简单实例

1. 事务执行时序表

事务(ID:41114),在索引idx_b值为4上加排他锁。

T1(41114)
begin;
select * from t where stage = 4 for update;

2. 查看InnoDB运行状态

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---TRANSACTION 41114, ACTIVE 41 sec
4 lock struct(s), heap size 1184, 3 row lock(s)
MySQL thread id 39, OS thread handle 0x700000a83000, query id 36756 localhost ::1 root cleaning up
TABLE LOCK table `test`.`t` trx id 41114 lock mode IX
RECORD LOCKS space id 245 page no 4 n bits 80 index `idx_b` of table `test`.`t` trx id 41114 lock_mode X
Record lock, heap no 7 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 80000004; asc ;;
1: len 4; hex 80000004; asc ;;
RECORD LOCKS space id 245 page no 3 n bits 80 index `PRIMARY` of table `test`.`t` trx id 41114 lock_mode X locks rec but not gap
Record lock, heap no 6 PHYSICAL RECORD: n_fields 4; compact format; info bits 0
0: len 4; hex 80000004; asc ;;
1: len 6; hex 00000000a08b; asc ;;
2: len 7; hex dd000001fa0110; asc ;;
3: len 4; hex 80000004; asc ;;
RECORD LOCKS space id 245 page no 4 n bits 80 index `idx_b` of table `test`.`t` trx id 41114 lock_mode X locks gap before rec
Record lock, heap no 8 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 80000009; asc ;;
1: len 4; hex 80000009; asc ;;

3. 解读InnoDB运行状态

事务T1总共加了4把锁:1把表,3把行锁。
表锁类型:IX

行锁根据索引划分为加在聚集索引 PRIMARY 上的行锁和加在普通索引 idx_b 上的行锁。
加在聚集索引上的行锁1把,是一个排他的记录锁;
加在普通索引上的行锁2把,1把是next-key lock,锁住的范围为(1, 4];1把是gap lock,锁住的范围为(4, 9)。

四、复杂实例

下面演示一个更加复杂的实例:GAP与Insert Intention冲突引发的死锁,分析死锁时各事务锁占用情况。

1. 事务执行时序表

T1(41121) T1(41122)
begin; begin;
select * from t where stage = 4 for update;
select * from t where stage = 9 for update;
insert INTO t values (6, 6)
insert INTO t values (7, 7)
(1213, u’Deadlock found when trying to get lock; try restarting transaction’)
Query OK, 1 row affected  

事务T1首先锁住stage=4的记录,然后插入(6, 6)的记录;
事务T2首先锁住stage=9的记录,然后插入(7, 7)的记录。

2. 查看InnoDB运行状态

由于发生死锁后,其中一个事务会回滚,而无法查看到其事务锁占用状态。
因此,我们在在事务T2执行记录插入操作之前,查看一下当前各事务锁占用状态。如下所示:

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------------
TRANSACTIONS
------------
Trx id counter 41123
Purge done for trx's n:o < 41120 undo n:o < 0 state: running but idle
History list length 968
LIST OF TRANSACTIONS FOR EACH SESSION:
---TRANSACTION 0, not started
MySQL thread id 67, OS thread handle 0x700000ac7000, query id 37547 localhost ::1 root init
show ENGINE innodb status
---TRANSACTION 41105, not started
MySQL thread id 65, OS thread handle 0x700000b0b000, query id 36363 localhost 127.0.0.1 root cleaning up
---TRANSACTION 0, not started
MySQL thread id 64, OS thread handle 0x700000b4f000, query id 36362 localhost 127.0.0.1 root cleaning up
---TRANSACTION 0, not started
MySQL thread id 58, OS thread handle 0x700000a3f000, query id 37546 localhost root cleaning up
---TRANSACTION 41122, ACTIVE 26 sec
4 lock struct(s), heap size 1184, 3 row lock(s)
MySQL thread id 69, OS thread handle 0x700000bd7000, query id 37534 localhost ::1 root cleaning up
TABLE LOCK table `test`.`t` trx id 41122 lock mode IX
RECORD LOCKS space id 245 page no 4 n bits 80 index `idx_b` of table `test`.`t` trx id 41122 lock_mode X
Record lock, heap no 8 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 80000009; asc ;;
1: len 4; hex 80000009; asc ;;
RECORD LOCKS space id 245 page no 3 n bits 80 index `PRIMARY` of table `test`.`t` trx id 41122 lock_mode X locks rec but not gap
Record lock, heap no 7 PHYSICAL RECORD: n_fields 4; compact format; info bits 0
0: len 4; hex 80000009; asc ;;
1: len 6; hex 00000000a08b; asc ;;
2: len 7; hex dd000001fa011d; asc ;;
3: len 4; hex 80000009; asc ;;
RECORD LOCKS space id 245 page no 4 n bits 80 index `idx_b` of table `test`.`t` trx id 41122 lock_mode X locks gap before rec
Record lock, heap no 9 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 8000000f; asc ;;
1: len 4; hex 8000000f; asc ;;
---TRANSACTION 41121, ACTIVE 34 sec inserting
mysql tables in use 1, locked 1
LOCK WAIT 5 lock struct(s), heap size 1184, 4 row lock(s), undo log entries 1
MySQL thread id 39, OS thread handle 0x700000a83000, query id 37538 localhost ::1 root update
insert INTO t values (6, 6)
------- TRX HAS BEEN WAITING 21 SEC FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 245 page no 4 n bits 80 index `idx_b` of table `test`.`t` trx id 41121 lock_mode X locks gap before rec insert intention waiting
Record lock, heap no 8 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 80000009; asc ;;
1: len 4; hex 80000009; asc ;;
------------------
TABLE LOCK table `test`.`t` trx id 41121 lock mode IX
RECORD LOCKS space id 245 page no 4 n bits 80 index `idx_b` of table `test`.`t` trx id 41121 lock_mode X
Record lock, heap no 7 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 80000004; asc ;;
1: len 4; hex 80000004; asc ;;
RECORD LOCKS space id 245 page no 3 n bits 80 index `PRIMARY` of table `test`.`t` trx id 41121 lock_mode X locks rec but not gap
Record lock, heap no 6 PHYSICAL RECORD: n_fields 4; compact format; info bits 0
0: len 4; hex 80000004; asc ;;
1: len 6; hex 00000000a08b; asc ;;
2: len 7; hex dd000001fa0110; asc ;;
3: len 4; hex 80000004; asc ;;
RECORD LOCKS space id 245 page no 4 n bits 80 index `idx_b` of table `test`.`t` trx id 41121 lock_mode X locks gap before rec
Record lock, heap no 8 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 80000009; asc ;;
1: len 4; hex 80000009; asc ;;
RECORD LOCKS space id 245 page no 4 n bits 80 index `idx_b` of table `test`.`t` trx id 41121 lock_mode X locks gap before rec insert intention waiting
Record lock, heap no 8 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 80000009; asc ;;
1: len 4; hex 80000009; asc ;;

3. 死锁日志

事务T2执行记录插入操作,发生死锁。
死锁日志如下所示:

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------------------------
LATEST DETECTED DEADLOCK
------------------------
2016-08-04 13:39:05 700000bd7000
*** (1) TRANSACTION:
TRANSACTION 41121, ACTIVE 54 sec inserting
mysql tables in use 1, locked 1
LOCK WAIT 5 lock struct(s), heap size 1184, 4 row lock(s), undo log entries 1
MySQL thread id 39, OS thread handle 0x700000a83000, query id 37538 localhost ::1 root update
insert INTO t values (6, 6)
*** (1) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 245 page no 4 n bits 80 index `idx_b` of table `test`.`t` trx id 41121 lock_mode X locks gap before rec insert intention waiting
Record lock, heap no 8 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 80000009; asc ;;
1: len 4; hex 80000009; asc ;;
*** (2) TRANSACTION:
TRANSACTION 41122, ACTIVE 46 sec inserting
mysql tables in use 1, locked 1
5 lock struct(s), heap size 1184, 4 row lock(s), undo log entries 1
MySQL thread id 69, OS thread handle 0x700000bd7000, query id 37555 localhost ::1 root update
insert INTO t values (7, 7)
*** (2) HOLDS THE LOCK(S):
RECORD LOCKS space id 245 page no 4 n bits 80 index `idx_b` of table `test`.`t` trx id 41122 lock_mode X
Record lock, heap no 8 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 80000009; asc ;;
1: len 4; hex 80000009; asc ;;
*** (2) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 245 page no 4 n bits 80 index `idx_b` of table `test`.`t` trx id 41122 lock_mode X locks gap before rec insert intention waiting
Record lock, heap no 8 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 80000009; asc ;;
1: len 4; hex 80000009; asc ;;
*** WE ROLL BACK TRANSACTION (2)

由上述死锁日志可知:两个事务都在等待加在这个位置的锁 space id 245 page no 4 n bits 80
另外,

4. 解读InnoDB运行状态

事务T1

事务T1总共 要加 5把锁:1把表,4把行锁。

表锁
表锁类型:IX

行锁
idx_b 上的排他 next-key lock,范围:idx_b in (1, 4]。
内存位置:space id 245 page no 4 n bits 80,heap no 7 PHYSICAL RECORD: n_fields 2;

primary 上的排他 record lock,范围:primary=4。
内存位置:space id 245 page no 3 n bits 80,heap no 6 PHYSICAL RECORD: n_fields 4;

idx_b 上的排他 gap lock,范围:idx_b in (4, 9)。
内存位置:space id 245 page no 4 n bits 80,heap no 8 PHYSICAL RECORD: n_fields 2;

idx_b 上的排他 insert intention lock,范围:idx_b in (4, 9)。
内存位置:space id 245 page no 4 n bits 80,heap no 8 PHYSICAL RECORD: n_fields 2;

其中,insert intention lock 是正等待加的锁。

事务T2

:当前分析事务T2占用的锁快照为T2执行插入语句之前状态。

事务T2总共加了4把锁:1把表,3把行锁。

表锁
表锁类型:IX

行锁
idx_b 上的排他 next-key lock,范围:idx_b in (4, 9]
内存位置:space id 245 page no 4 n bits 80,heap no 8 PHYSICAL RECORD: n_fields 2;

primary 上的排他 record lock,范围:primary=9
内存位置:space id 245 page no 3 n bits 80,heap no 7 PHYSICAL RECORD: n_fields 4;

idx_b 上的排他 gap lock,范围:idx_b in (9, 15)
内存位置:space id 245 page no 4 n bits 80,heap no 9 PHYSICAL RECORD: n_fields 2;

死锁分析

在事务T1插入记录前,事务T1拿到了范围idx_b in (4, 9)的gap lock,事务T2拿到了范围idx_b in (4, 9]上的next-key lock。

事务T1插入记录(6, 6)时,要请求范围idx_b in (4, 9)上的insert intention lock,而请求的insert intention lock与事务T2已持有next key lock是互斥的。
于是,事务T1 block,等待事务T2释放范围idx_b in (4, 9]上的next-key lock。

事务T2插入记录(7, 7)时,要请求范围idx_b in (4, 9)上的insert intention lock,而请求的insert intention lock与事务T1已持有的gap lock是互斥的。
于是,事务T2也会block,等待事务T2释放范围idx_b in (4, 9)上的gap lock。
死锁便产生了。

文章目录
  1. 一、表结构
  2. 二、表数据
  3. 三、简单实例
    1. 1. 事务执行时序表
    2. 2. 查看InnoDB运行状态
    3. 3. 解读InnoDB运行状态
  4. 四、复杂实例
    1. 1. 事务执行时序表
    2. 2. 查看InnoDB运行状态
    3. 3. 死锁日志
    4. 4. 解读InnoDB运行状态
      1. 事务T1
      2. 事务T2
      3. 死锁分析
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