高并发下，php与redis实现的抢购、秒杀功能

抢购、秒杀是现在很常见的一个应用场景，主要须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小（"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，避免直接操做数据库，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，而后执行生成订单等操做，可是在判断库存是否大于0处，若是在高并发下就会有问题，致使库存量出现负数

<?php $conn=mysqli_connect("localhost","root",""); if(!$conn){ echo "connect failed"; exit; } mysqli_select_db($conn,"ceshi"); mysqli_query($conn,"set names utf8"); $price=10; $user_id=1; $goods_id=1; $sku_id=11; $number=1; //生成惟一订单
function build_order_no(){ return date('ymd').substr(implode(NULL, array_map('ord', str_split(substr(uniqid(), 7, 13), 1))), 0, 8); } //记录日志
function insertLog($event,$type=0){ global $conn; $sql="insert into ih_log(event,type) values('$event','$type')"; mysqli_query($conn,$sql); } //模拟下单操做 //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)，其它事务必须等待这次事务 提交后才能执行
$rs=mysqli_query($conn,$sql); $row=mysqli_fetch_assoc($rs); if($row['number']>0){//高并发下会致使超卖
$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); //库存减小
$sql="update ih_store set number=number-{$number} where sku_id='$sku_id'"; $store_rs=mysqli_query($conn,$sql); if(mysqli_affected_rows($conn)){ insertLog('库存减小成功'); }else{ insertLog('库存减小失败'); } }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，由于字段不能为负数，将会返回false //库存减小
$sql="update ih_store set number=number-{$number} where sku_id='$sku_id' and number>0"; $store_rs=mysql_query($sql,$conn); if(mysql_affected_rows()){ insertLog('库存减小成功'); }

 

优化方案2：使用MySQL的事务，锁住操做的行

<?php $conn=mysqli_connect("localhost","root",""); if(!$conn){ echo "connect failed"; exit; } mysqli_select_db($conn,"ceshi"); mysqli_query($conn,"set names utf8"); $price=10; $user_id=1; $goods_id=1; $sku_id=11; $number=1; //生成惟一订单号
function build_order_no(){ return date('ymd').substr(implode(NULL, array_map('ord', str_split(substr(uniqid(), 7, 13), 1))), 0, 8); } //记录日志
function insertLog($event,$type=0){ global $conn; $sql="insert into ih_log(event,type) values('$event','$type')"; mysqli_query($conn,$sql); } //模拟下单操做 //库存是否大于0
mysqli_query($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,其它事务必须等待这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); //库存减小
    $sql="update ih_store set number=number-{$number} where sku_id='$sku_id'"; $store_rs=mysqli_query($conn,$sql); if(mysqli_affected_rows($conn)){ insertLog('库存减小成功'); mysqli_query($conn,"COMMIT");//事务提交即解锁
    }else{ insertLog('库存减小失败'); } }else{ insertLog('库存不够'); mysqli_query($conn,"ROLLBACK"); } ?>

 

优化方案3：使用非阻塞的文件排他锁

<?php $conn=mysqli_connect("localhost","root",""); if(!$conn){ echo "connect failed"; exit; } mysqli_select_db($conn,"ceshi"); mysqli_query($conn,"set names utf8"); $price=10; $user_id=1; $goods_id=1; $sku_id=11; $number=1; //生成惟一订单号
function build_order_no(){ return date('ymd').substr(implode(NULL, array_map('ord', str_split(substr(uniqid(), 7, 13), 1))), 0, 8); } //记录日志
function insertLog($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 //模拟下单操做 
    $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); //库存减小
    $sql="update ih_store set number=number-{$number} where sku_id='$sku_id'"; $store_rs=mysqli_query($conn,$sql); if(mysqli_affected_rows($conn)){ insertLog('库存减小成功'); flock($fp,LOCK_UN);//释放锁
    }else{ insertLog('库存减小失败'); } }else{ insertLog('库存不够'); } fclose($fp);

 

优化方案4：使用redis队列，由于pop操做是原子的，即便有不少用户同时到达，也是依次执行，推荐使用（mysql事务在高并发下性能降低很厉害，文件锁的方式也是）

先将商品库存如队列

<?php $store=1000; $redis=new Redis(); $result=$redis->connect('127.0.0.1',6379); $res=$redis->llen('goods_store'); echo $res; $count=$store-$res; for($i=0;$i<$count;$i++){ $redis->lpush('goods_store',1); } echo $redis->llen('goods_store'); ?>

抢购、描述逻辑

<?php $conn=mysqli_connect("localhost","root",""); if(!$conn){ echo "connect failed"; exit; } mysqli_select_db($conn,"ceshi"); mysqli_query($conn,"set names utf8"); $price=10; $user_id=1; $goods_id=1; $sku_id=11; $number=1; //生成惟一订单号
function build_order_no(){ return date('ymd').substr(implode(NULL, array_map('ord', str_split(substr(uniqid(), 7, 13), 1))), 0, 8); } //记录日志
function insertLog($event,$type=0){ global $conn; $sql="insert into ih_log(event,type) values('$event','$type')"; mysqli_query($conn,$sql); } //模拟下单操做 //下单前判断redis队列库存量
$redis=new Redis(); $result=$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); //库存减小
$sql="update ih_store set number=number-{$number} where sku_id='$sku_id'"; $store_rs=mysqli_query($conn,$sql); if(mysqli_affected_rows()){ insertLog('库存减小成功'); }else{ insertLog('库存减小失败'); }

 

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不少，不少注意的地方

如抢购页面作成静态的，经过ajax调用接口

再如上面的会致使一个用户抢多个，思路：

须要一个排队队列和抢购结果队列及库存队列。高并发状况，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，若是在，则已抢购，不然未抢购，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 TABLE IF NOT EXISTS `ih_goods` ( `goods_id` int(10) unsigned NOT NULL AUTO_INCREMENT, `cat_id` int(11) NOT NULL, `goods_name` varchar(255) NOT NULL, PRIMARY KEY (`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 TABLE IF NOT EXISTS `ih_log` ( `id` int(11) NOT NULL AUTO_INCREMENT, `event` varchar(255) NOT NULL, `type` tinyint(4) NOT NULL DEFAULT '0', `addtime` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP, PRIMARY KEY (`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 TABLE IF NOT 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 NOT NULL DEFAULT CURRENT_TIMESTAMP, PRIMARY KEY (`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 TABLE IF NOT 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', PRIMARY KEY (`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);