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