日期:2014-05-16  浏览次数:20778 次

mysql行锁和表锁

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在调用存储过程中,就会涉及到表锁,行锁这一概念:所谓区别:有索引的时候就是行锁,没有索引的时候就是表索。

innodb 的行锁是在有索引的情况下,没有索引的表是锁定全表的.

表锁演示(无索引)

Session1:

mysql> set autocommit=0;

mysql> select * from innodb_test;
+------+-------------+
| id?? | name??????? |
+------+-------------+
|??? 1 | woshiceshi? |?
|??? 2 | woshiceshi2 |?
|??? 3 | woshiceshi3 |?
+------+-------------+

mysql> select * from innodb_test where id = 2 for update;
+------+------------+
| id?? | name?????? |
+------+------------+
|??? 2 | woshiceshi2 |?
+------+------------+

Session2:

mysql> update innodb_test set name='sjis' where id = 1 ;
处于等待状态....

再回到session1 commit以后,session2就出来结果了(锁定了8秒,过了8秒左右才去session1提交)。

mysql> update innodb_test set name='sjis' where id = 1 ;
Query OK, 1 row affected (8.11 sec)
Rows matched: 1? Changed: 1? Warnings: 0

实验结果是:我在session1的for update 操作看似只锁定ID为2的行其实锁定了全表,以至于后面session2的对ID为1的行update 需要等待Session1锁的释放。

行锁演示(索引为ID)

Session1:
mysql> alter table innodb_test add index idx_id(id);
Query OK, 4 rows affected (0.01 sec)
Records: 4? Duplicates: 0? Warnings: 0

mysql> select * from innodb_test where id = 2 for update;
+------+------------+
| id?? | name?????? |
+------+------------+
|??? 2 | woshiceshi2 |?
+------+------------+

Session2:

mysql> update innodb_test set name='wohaishiceshi' where id = 1 ;
Query OK, 1 row affected (0.02 sec)
Rows matched: 1? Changed: 1? Warnings: 0
mysql> select * from innodb_test where id = 1;???????????
+------+---------------+
| id?? | name????????? |
+------+---------------+
|??? 1 | wohaishiceshi |?
+------+---------------+
1 row in set (0.00 sec)

实验结果:这次的锁定是锁定的行,所以没有被锁定的行(ID不为2的行)可以进行update..