PHP利用Mysql锁解决高并发

前面写过利用文件锁来处理高并发的问题的，现在我们说另外一个处理方式，利用Mysql的锁来解决高并发的问题

先看没有利用事务的时候并发的后果

创建库存管理表

```
CREATE TABLE `storage` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`number` int(11) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=latin1
```

创建订单管理表

```
CREATE TABLE `order` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`number` int(11) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=34 DEFAULT CHARSET=latin1
```

测试代码

$pdo = new PDO('mysql:host=127.0.0.1;port=3306; dbname=test','root','123456');
$sql="select `number` from  storage where id=1 limit 1";
$res = $pdo->query($sql)->fetch();
$number = $res['number'];

if($number>0)
{
    $sql ="insert into `order`  VALUES (null,$number)";

    $order_id = $pdo->query($sql);
    if($order_id)
    {

        $sql="update storage set `number`=`number`-1 WHERE id=1";
        $pdo->query($sql);
    }
}

我们预置库存是十个，然后执行ab测试查看结果

```
mysql> select * from storage
-> ;
+----+--------+
| id | number |
+----+--------+
| 1 | -2 |
+----+--------+
1 row in set (0.00 sec)

mysql> select * from order;

+----+--------+

| id | number |

+----+--------+

| 22 | 10 |

| 23 | 10 |

| 24 | 8 |

| 25 | 8 |

| 26 | 7 |

| 27 | 6 |

| 28 | 4 |

| 29 | 3 |

| 30 | 2 |

| 31 | 2 |

| 32 | 2 |

| 33 | 1 |

+----+--------+

12 rows in set (0.00 sec)

<p>得到了订单共有<code>12</code>个，而库存表的库存也减到了<code>-2</code>，这显然不符合实际逻辑的;</p>
<h5>下面我们来看利用数据库行锁来解决这个问题</h5>
<blockquote>修改代码如下</blockquote>

$pdo = new PDO('mysql:host=127.0.0.1;port=3306; dbname=test','root','123456');

$pdo->beginTransaction();//开启事务

$sql="select number from storage where id=1 for UPDATE ";//利用for update 开启行锁

$res = $pdo->query($sql)->fetch();

$number = $res['number'];

if($number>0)

{

$sql ="insert into order VALUES (null,$number)";

$order_id = $pdo->query($sql);
if($order_id)
{

    $sql="update storage set `number`=`number`-1 WHERE id=1";
    if($pdo->query($sql))
    {
        $pdo->commit();//提交事务
    }
    else
    {
        $pdo->rollBack();//回滚
    }

}
else
{
    $pdo->rollBack();//回滚
}

}

<blockquote>查看结果</blockquote>

mysql> select * from storage;

+----+--------+

| id | number |

+----+--------+

| 1 | 0 |

+----+------

--+

1 row in set (0.00 sec)

mysql> select * from order;

+----+--------+

| id | number |

+----+--------+

| 1 | 10 |

| 2 | 9 |

| 3 | 8 |

| 4 | 7 |

| 5 | 6 |

| 6 | 5 |

| 7 | 4 |

| 8 | 3 |

| 9 | 2 |

| 10 | 1 |

+----+--------+

10 rows in set (0.00 sec)

<p>很明显在利用了mysql锁之后，对库存进行了有效的控制，很好的解决了第一段代码里面，因为并发引起的一些逻辑性的问题</p>

原文地址：https://segmentfault.com/a/1190000016251947