抢购、秒杀是如今很常见的一个应用场景,主要需要解决的问题有两个:
1 高并发对数据库产生的压力
2 竞争状态下如何解决库存的正确减少("超卖"问题)
对于第一个问题,已经很容易想到用缓存来处理抢购,避免直接操作数据库,例如使用Redis。
重点在于第二个问题
常规写法:
查询出对应商品的库存,看是否大于0,然后执行生成订单等操作,但是在判断库存是否大于0处,如果在高并发下就会有问题,导致库存量出现负数
}mysqli_select_db($conn,"ceshi");mysqli_query($conn,"set names utf8");$price=10;$user_id=1;$goods_id=1;$sku_id=11;$number=1;//生成唯一订单
functionbuild_order_no(){return date('ymd').substr(implode(NULL, array_map('ord', str_split(substr(uniqid(), 7, 13), 1))), 0, 8);
}//记录日志
function insertLog($event,$type=0){global $conn;$sql="insert into ih_log(event,type)
values('$event','$type')";mysqli_query($conn,$sql);
}//模拟下单操作
//库存是否大于0
$sql="select number from ih_store where goods_id='$goods_id' and sku_id='$sku_id'";//解锁 此时ih_store数据中goods_id='$goods_id' and sku_id='$sku_id' 的数据被锁住(注3),其它事务必须等待此次事务 提交后才能执行
$rs=mysqli_query($conn,$sql);$row=mysqli_fetch_assoc($rs);if($row['number']>0){//高并发下会导致超卖
$order_sn=build_order_no();//生成订单
$sql="insert into ih_order(order_sn,user_id,goods_id,sku_id,price)
values('$order_sn','$user_id','$goods_id','$sku_id','$price')";$order_rs=mysqli_query($conn,$sql);//库存减少
$sql="update ih_store set number=number-{$number} where sku_id='$sku_id'";$store_rs=mysqli_query($conn,$sql);if(mysqli_affected_rows($conn)){
insertLog('库存减少成功');
}else{
insertLog('库存减少失败');
}
}else{
insertLog('库存不够');
}?>优化方案1:将库存字段number字段设为unsigned,当库存为0时,因为字段不能为负数,将会返回false//库存减少
$sql="update ih_store set number=number-{$number} where sku_id='$sku_id' and number>0";$store_rs=mysql_query($sql,$conn);if(mysql_affected_rows()){
insertLog('库存减少成功');
}
优化方案2:使用MySQL的事务,锁住操作的行
}mysqli_select_db($conn,"ceshi");mysqli_query($conn,"set names utf8");$price=10;$user_id=1;$goods_id=1;$sku_id=11;$number=1;//生成唯一订单号
functionbuild_order_no(){return date('ymd').substr(implode(NULL, array_map('ord', str_split(substr(uniqid(), 7, 13), 1))), 0, 8);
}//记录日志
function insertLog($event,$type=0){global $conn;$sql="insert into ih_log(event,type)
values('$event','$type')";mysqli_query($conn,$sql);
}//模拟下单操作
//库存是否大于0
mysqli_query($conn,"BEGIN"); //开始事务
$sql="select number from ih_store where goods_id='$goods_id' and sku_id='$sku_id' FOR UPDATE";//此时这条记录被锁住,其它事务必须等待此次事务提交后才能执行
$rs=mysqli_query($conn,$sql);$row=mysqli_fetch_assoc($rs);if($row['number']>0){//生成订单
$order_sn=build_order_no();$sql="insert into ih_order(order_sn,user_id,goods_id,sku_id,price)
values('$order_sn','$user_id','$goods_id','$sku_id','$price')";$order_rs=mysqli_query($conn,$sql);//库存减少
$sql="update ih_store set number=number-{$number} where sku_id='$sku_id'";$store_rs=mysqli_query($conn,$sql);if(mysqli_affected_rows($conn)){
insertLog('库存减少成功');mysqli_query($conn,"COMMIT");//事务提交即解锁
}else{
insertLog('库存减少失败');
}
}else{
insertLog('库存不够');mysqli_query($conn,"ROLLBACK");
}?>
优化方案3:使用非阻塞的文件排他锁
}mysqli_select_db($conn,"ceshi");mysqli_query($conn,"set names utf8");$price=10;$user_id=1;$goods_id=1;$sku_id=11;$number=1;//生成唯一订单号
functionbuild_order_no(){return date('ymd').substr(implode(NULL, array_map('ord', str_split(substr(uniqid(), 7, 13), 1))), 0, 8);
}//记录日志
function insertLog($event,$type=0){global $conn;$sql="insert into ih_log(event,type)
values('$event','$type')";mysqli_query($conn,$sql);
}$fp = fopen("lock.txt", "w+");if(!flock($fp,LOCK_EX |LOCK_NB)){echo "系统繁忙,请稍后再试";return;
}//下单
$sql="select number from ih_store where goods_id='$goods_id' and sku_id='$sku_id'";$rs=mysqli_query($conn,$sql);$row=mysqli_fetch_assoc($rs);if($row['number']>0){//库存是否大于0
//模拟下单操作
$order_sn=build_order_no();$sql="insert into ih_order(order_sn,user_id,goods_id,sku_id,price)
values('$order_sn','$user_id','$goods_id','$sku_id','$price')";$order_rs=mysqli_query($conn,$sql);//库存减少
$sql="update ih_store set number=number-{$number} where sku_id='$sku_id'";$store_rs=mysqli_query($conn,$sql);if(mysqli_affected_rows($conn)){
insertLog('库存减少成功');flock($fp,LOCK_UN);//释放锁
}else{
insertLog('库存减少失败');
}
}else{
insertLog('库存不够');
}fclose($fp);
优化方案4:使用redis队列,因为pop操作是原子的,即使有很多用户同时到达,也是依次执行,推荐使用(mysql事务在高并发下性能下降很厉害,文件锁的方式也是)
先将商品库存如队列
<?php $store=1000;$redis=newRedis();$result=$redis->connect('127.0.0.1',6379);$res=$redis->llen('goods_store');echo $res;$count=$store-$res;for($i=0;$ilpush('goods_store',1);
}echo $redis->llen('goods_store');?>
抢购、描述逻辑
}mysqli_select_db($conn,"ceshi");mysqli_query($conn,"set names utf8");$price=10;$user_id=1;$goods_id=1;$sku_id=11;$number=1;//生成唯一订单号
functionbuild_order_no(){return date('ymd').substr(implode(NULL, array_map('ord', str_split(substr(uniqid(), 7, 13), 1))), 0, 8);
}//记录日志
function insertLog($event,$type=0){global $conn;$sql="insert into ih_log(event,type)
values('$event','$type')";mysqli_query($conn,$sql);
}//模拟下单操作
//下单前判断redis队列库存量
$redis=newRedis();$result=$redis->connect('127.0.0.1',6379);$count=$redis->lpop('goods_store');if(!$count){
insertLog('error:no store redis');return;
}//生成订单
$order_sn=build_order_no();$sql="insert into ih_order(order_sn,user_id,goods_id,sku_id,price)
values('$order_sn','$user_id','$goods_id','$sku_id','$price')";$order_rs=mysqli_query($conn,$sql);//库存减少
$sql="update ih_store set number=number-{$number} where sku_id='$sku_id'";$store_rs=mysqli_query($conn,$sql);if(mysqli_affected_rows()){
insertLog('库存减少成功');
}else{
insertLog('库存减少失败');
}
模拟5000高并发测试
webbench -c 5000 -t 60 http://192.168.1.198/big/index.php
ab -r -n 6000 -c 5000 http://192.168.1.198/big/index.php
上述只是简单模拟高并发下的抢购,真实场景要比这复杂很多,很多注意的地方
如抢购页面做成静态的,通过ajax调用接口
再如上面的会导致一个用户抢多个,思路:
需要一个排队队列和抢购结果队列及库存队列。高并发情况,先将用户进入排队队列,用一个线程循环处理从排队队列取出一个用户,判断用户是否已在抢购结果队列,如果在,则已抢购,否则未抢购,库存减1,写数据库,将用户入结果队列。
测试数据表
--
-- 数据库:`big`--
-- --------------------------------------------------------
--
--表的结构 `ih_goods`--CREATE TABLEIFNOT EXISTS `ih_goods` (
`goods_id` int(10) unsigned NOT NULL AUTO_INCREMENT,`cat_id` int(11) NOT NULL,`goods_name` varchar(255) NOT NULL,PRIMARYKEY(`goods_id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=2;--
--转存表中的数据 `ih_goods`--INSERT INTO `ih_goods` (`goods_id`, `cat_id`,`goods_name`) VALUES
(1, 0, '小米手机');-- --------------------------------------------------------
--
--表的结构 `ih_log`--CREATE TABLEIFNOT EXISTS `ih_log` (
`id` int(11) NOT NULL AUTO_INCREMENT,`event` varchar(255) NOT NULL,`type` tinyint(4) NOT NULL DEFAULT '0',`addtime` timestamp NOTNULL DEFAULT CURRENT_TIMESTAMP,PRIMARYKEY(`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=1;--
--转存表中的数据 `ih_log`--
-- --------------------------------------------------------
--
--表的结构 `ih_order`--CREATE TABLEIFNOT EXISTS `ih_order` (
`id` int(11) NOT NULL AUTO_INCREMENT,`order_sn` char(32) NOT NULL,`user_id` int(11) NOT NULL,`status` int(11) NOT NULL DEFAULT '0',`goods_id` int(11) NOT NULL DEFAULT '0',`sku_id` int(11) NOT NULL DEFAULT '0',`price`float NOT NULL,`addtime` timestamp NOTNULL DEFAULT CURRENT_TIMESTAMP,PRIMARYKEY(`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='订单表' AUTO_INCREMENT=1;--
--转存表中的数据 `ih_order`--
-- --------------------------------------------------------
--
--表的结构 `ih_store`--CREATE TABLEIFNOT EXISTS `ih_store` (
`id` int(11) NOT NULL AUTO_INCREMENT,`goods_id` int(11) NOT NULL,`sku_id` int(10) unsigned NOT NULL DEFAULT '0',`number` int(10) NOT NULL DEFAULT '0',`freez` int(11) NOT NULL DEFAULT '0' COMMENT '虚拟库存',PRIMARYKEY(`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='库存' AUTO_INCREMENT=2;--
--转存表中的数据 `ih_store`--INSERT INTO `ih_store` (`id`, `goods_id`, `sku_id`, `number`,`freez`) VALUES
(1, 1, 11, 500, 0);