唯一约束锁分析

MySQL：8.0.20 MySQL Community Server - GPL

隔离级别：RC

8版中本有performance.schema.data_locks 表，方便分析锁问题

创建测试数据：

mysql> show create table t1G
*************************** 1. row ***************************
       Table: t1
Create Table: CREATE TABLE `t1` (
  `id` int NOT NULL AUTO_INCREMENT,
  `od` int DEFAULT NULL,
  `name` varchar(200) DEFAULT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `od` (`od`)
) ENGINE=InnoDB AUTO_INCREMENT=101 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

mysql> insert into t1(id,od,name) values(1,1,'a'),(2,2,'b'),(3,3,'c'),(4,4,'d'),(100,100,'fff');

1、insert 唯一键不冲突

mysql> begin;
Query OK, 0 rows affected (0.00 sec)

mysql> insert into t1(id,od,name) values(50,50,'def');
Query OK, 1 row affected (0.00 sec)

performance.schema.data_locks 表 查询结果如下

库名	表名	INDEX_NAME	lock_type	lock_mode	LOCK_STATUS	LOCK_DATA
ceshi	t1	NULL	TABLE	IX	GRANTED	NULL

2、insert into 主键冲突

mysql> begin;
Query OK, 0 rows affected (0.01 sec)

mysql> insert into t1(id,od,name) values(4,4,'d');
ERROR 1062 (23000): Duplicate entry '4' for key 't1.PRIMARY'

库名	表名	INDEX_NAME	lock_type	lock_mode	LOCK_STATUS	LOCK_DATA
ceshi	t1	NULL	TABLE	IX	GRANTED	NULL
ceshi	t1	PRIMARY	RECORD	S,REC_NOT_GAP	GRANTED	4

3、insert into 唯一约束冲突

mysql> begin;
Query OK, 0 rows affected (0.00 sec)

mysql> insert into t1(id,od,name) values(400,4,'d');
ERROR 1062 (23000): Duplicate entry '4' for key 't1.od'

库名	表名	INDEX_NAME	lock_type	lock_mode	LOCK_STATUS	LOCK_DATA
ceshi	t1	NULL	TABLE	IX	GRANTED	NULL
ceshi	t1	od	RECORD	S	GRANTED	4

4、replace into ... 主键/唯一约束冲突

mysql> begin;
Query OK, 0 rows affected (0.00 sec)

mysql> replace into t1(id,od,name) values(4,4,'ddddd');
Query OK, 2 rows affected (0.00 sec)

库名	表名	INDEX_NAME	lock_type	lock_mode	LOCK_STATUS	LOCK_DATA
ceshi	t1	NULL	TABLE	IX	GRANTED	NULL
ceshi	t1	PRIMARY	RECORD	X,REC_NOT_GAP	GRANTED	4
ceshi	t1	od	RECORD	X,REC_NOT_GAP	GRANTED	4
ceshi	t1	od	RECORD	X,GAP	GRANTED	4, 4
ceshi	t1	od	RECORD	X	GRANTED	100, 100

5、replace into ... 唯一约束冲突

mysql> begin;
Query OK, 0 rows affected (0.00 sec)

mysql> replace into t1(id,od,name) values(null,4,'ddddd');
Query OK, 2 rows affected (0.00 sec)

库名	表名	INDEX_NAME	lock_type	lock_mode	LOCK_STATUS	LOCK_DATA
ceshi	t1	NULL	TABLE	IX	GRANTED	NULL
ceshi	t1	od	RECORD	X	GRANTED	4, 4
ceshi	t1	od	RECORD	X	GRANTED	100, 100
ceshi	t1	PRIMARY	RECORD	X,REC_NOT_GAP	GRANTED	4
ceshi	t1	od	RECORD	X,GAP	GRANTED	4, 101

6、同一事务 delete / insert into 唯一约束

库名	表名	INDEX_NAME	lock_type	lock_mode	LOCK_STATUS	LOCK_DATA
ceshi	t1	NULL	TABLE	IX	GRANTED	NULL
ceshi	t1	od	RECORD	X,REC_NOT_GAP	GRANTED	4, 4
ceshi	t1	od	PRIMARY	X,REC_NOT_GAP	GRANTED	4
ceshi	t1	od	RECORD	S,GAP	GRANTED	4, 4
ceshi	t1	od	RECORD	S	GRANTED	100, 100