一.数据准备
mysql> use test;
Database changed
mysql> show create table t_kenyon \G
*************************** 1. row ***************************
       Table: t_kenyon
Create Table: CREATE TABLE `t_kenyon` (
  `id` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
 
mysql> set autocommit = 0;
Query OK, 0 rows affected (0.00 sec)
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mysql> show variables like '%autocommit%';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| autocommit    | OFF   |
+---------------+-------+
1 row in set (0.00 sec)
 
mysql> select * from t_kenyon;
+------+
| id   |
+------+
|    1 |
|  123 |
|  789 |
|  345 |
|   78 |
|   78 |
+------+
6 rows in set (0.00 sec)
以上是测试表t_kenyon,设置提交方式为手动提交. 
 
二.过程(开启两个session,分别设置autocommit=off) 
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1.session one update
mysql> update t_kenyon set id = 999 where id = 1;
Query OK, 1 row affected (0.04 sec)
Rows matched: 1  Changed: 1  Warnings: 0
 
mysql> select * from t_kenyon;
+------+
| id   |
+------+
|  999 |
|  123 |
|  789 |
|  345 |
|   78 |
|   78 |
+------+
6 rows in set (0.00 sec)
2.session two update
mysql> show variables like 'autocommit';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| autocommit    | OFF   |
+---------------+-------+
1 row in set (0.00 sec)
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mysql> select * from t_kenyon;
+------+
| id   |
+------+
|    1 |
|  123 |
|  789 |
|  345 |
|   78 |
|   78 |
+------+
6 rows in set (0.00 sec)
 
mysql> update t_kenyon set id = 88888 where id = 345;
第二个session更新的值是345，但是也一直被阻塞，直到session1被rollback或者commit,如果session1未做回滚或者提交，session2中的该阻塞在超出mysql的锁时间限制时自动回滚,该参数为innodb_lock_wait_timeout，默认值50秒 现象如下
ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
加索引后的测试 
3.session one update
 
mysql> create index ind_kenyon on t_kenyon(id);
Query OK, 0 rows affected (28.58 sec)
Records: 0  Duplicates: 0  Warnings: 0
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mysql> update t_kenyon set id = 999 where id = 1;
Query OK, 1 row affected (0.03 sec)
Rows matched: 1  Changed: 1  Warnings: 0
 
mysql> select * from t_kenyon;
+------+
| id   |
+------+
|   78 |
|   78 |
|  123 |
|  345 |
|  789 |
|  999 |
+------+
6 rows in set (0.00 sec)
4.session two update
 mysql> select * from t_kenyon;
+------+
| id   |
+------+
|    1 |
|   78 |
|   78 |
|  123 |
|  345 |
|  789 |
+------+
6 rows in set (0.00 sec)
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mysql> update t_kenyon set id = 7777 where id = 345;
Query OK, 1 row affected (0.03 sec)
Rows matched: 1  Changed: 1  Warnings: 0
 
mysql> select * from t_kenyon;
+------+
| id   |
+------+
|    1 |
|   78 |
|   78 |
|  123 |
|  789 |
| 7777 |
+------+
6 rows in set (0.00 sec)
执行计划
mysql> explain select * from t_kenyon where id = 345 \G
*************************** 1. row ***************************
           id: 1  www.2cto.com  
  select_type: SIMPLE
        table: t_kenyon
         type: ref
possible_keys: ind_kenyon
          key: ind_kenyon
      key_len: 5
          ref: const
         rows: 1
        Extra: Using where; Using index
1 row in set (0.00 sec)
可以看到加了索引后，不同的数据更新并没有被阻塞，实现了真正意义上行锁