PHP利用Mysql锁解决高并发的方法

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)

得到了订单共有12个，而库存表的库存也减到了-2，这显然不符合实际逻辑的;

下面我们来看利用数据库行锁来解决这个问题

修改代码如下

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

查看结果

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)