Innodb的行级锁的特性

Innodb的行级锁依赖于索引，如果条件字段上没有索引，将会锁定全表。

小实验

SESSION1:

mysql> create table t1 ( id int ) ;
Query OK, 0 rows affected (0.09 sec)

mysql> insert into t1 values(1 ), (2), ( 3) ;
Query OK, 3 rows affected (0.00 sec)
Records: 3 Duplicates: 0 Warnings: 0

mysql> select * from t1 ;
+------+
| id |
+------+
| 1 |
| 2 |
| 3 |
+------+
3 rows in set (0.00 sec)
SESSION2:

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

mysql> update t1 set id = 4 where id = 1 ; #这时会给整个表加写锁！！因为没有索引
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
SESSION1:

mysql> update t1 set id = 5 where id = 2 ;
出现等待。

 

SESSION2：

mysql> commit ;
Query OK, 0 rows affected (0.00 sec) 
SESSION1：

阻塞消失。

Query OK, 1 row affected (14.17 sec)

Rows matched: 1  Changed: 1  Warnings: 0