⾼并发下，php与redis实现的抢购、秒杀功能
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
<?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;
$number=1;
//⽣成唯⼀订单
function build_order_no(){
return date('ymd').substr(implode(NULL, array_map('ord', str_split(substr(uniqid(), 7, 13), 1))), 0, 8);
}
//记录⽇志
function insertLog($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
<?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;
$number=1;
//⽣成唯⼀订单号
function build_order_no(){
return date('ymd').substr(implode(NULL, array_map('ord', str_split(substr(uniqid(), 7, 13), 1))), 0, 8);
}
//记录⽇志
function insertLog($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
<?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;
$number=1;
//⽣成唯⼀订单号
function build_order_no(){
return date('ymd').substr(implode(NULL, array_map('ord', str_split(substr(uniqid(), 7, 13), 1))), 0, 8);
}
//记录⽇志
function insertLog($event,$type=0){
global$conn;
$sql="insert into ih_log(event,type)
values('$event','$type')";
mysqli_query($conn,$sql);
}
$fp = fopen("", "w+");
if(!flock($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=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;
$number=1;
//⽣成唯⼀订单号
function build_order_no(){
return date('ymd').substr(implode(NULL, array_map('ord', str_split(substr(uniqid(), 7, 13), 1))), 0, 8);
}
//记录⽇志
function insertLog($event,$type=0){
global$conn;
$sql="insert into ih_log(event,type)
values('$event','$type')";
mysqli_query($conn,$sql);
}
//模拟下单操作
//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');
php调用mysql数据库}else{
insertLog('库存减少失败');
}
模拟5000⾼并发测试
webbench -c 5000 -t 60 192.168.1.198/big/index.php
ab -r -n 6000 -c 5000 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 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);
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