PHP和Redis实现在高并发下的抢购及秒杀功能示例详解
抢购、秒杀是平常很常见的场景,面试的时候面试官也经常会问到,比如问你淘宝中的抢购秒杀是怎么实现的等等。
抢购、秒杀实现很简单,但是有些问题需要解决,主要针对两个问题:
一、高并发对数据库产生的压力
二、竞争状态下如何解决库存的正确减少("超卖"问题)
第一个问题,对于PHP来说很简单,用缓存技术就可以缓解数据库压力,比如memcache,redis等缓存技术。
第二个问题就比较复杂点:
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
$conn = mysql_connect("localhost", "big", "123456");
if (!$conn) {
echo "connect failed";
exit;
}
mysql_select_db("big", $conn);
mysql_query("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','$type')";
mysql_query($sql, $conn);
}
//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
$rs = mysql_query($sql, $conn);
$row = mysql_fetch_assoc($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')";
$order_rs = mysql_query($sql, $conn);
//库存减少
$sql = "update ih_store set number=number-{$number} where sku_id='$sku_id'";
$store_rs = mysql_query($sql, $conn);
if (mysql_affected_rows()) {
insertLog('库存减少成功');
} else {
insertLog('库存减少失败');
}
} else {
insertLog('库存不够');
}
出现这种情况怎么办呢?来看几种优化方法:
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
$conn = mysql_connect("localhost", "big", "123456");
if (!$conn) {
echo "connect failed";
exit;
}
mysql_select_db("big", $conn);
mysql_query("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','$type')";
mysql_query($sql, $conn);
}
//模拟下单操作
//库存是否大于0
mysql_query("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
$rs = mysql_query($sql, $conn);
$row = mysql_fetch_assoc($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')";
$order_rs = mysql_query($sql, $conn);
//库存减少
$sql = "update ih_store set number=number-{$number} where sku_id='$sku_id'";
$store_rs = mysql_query($sql, $conn);
if (mysql_affected_rows()) {
insertLog('库存减少成功');
mysql_query("COMMIT");//事务提交即解锁
} else {
insertLog('库存减少失败');
}
} else {
insertLog('库存不够');
mysql_query("ROLLBACK");
}
优化方案3:使用非阻塞的文件排他锁
<?php
$conn = mysql_connect("localhost", "root", "123456");
if (!$conn) {
echo "connect failed";
exit;
}
mysql_select_db("big-bak", $conn);
mysql_query("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','$type')";
mysql_query($sql, $conn);
}
$fp = fopen("lock.txt", "w+");
if (!flock($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'";
$rs = mysql_query($sql, $conn);
$row = mysql_fetch_assoc($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')";
$order_rs = mysql_query($sql, $conn);
//库存减少
$sql = "update ih_store set number=number-{$number} where sku_id='$sku_id'";
$store_rs = mysql_query($sql, $conn);
if (mysql_affected_rows()) {
insertLog('库存减少成功');
flock($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
$conn = mysql_connect("localhost", "big", "123456");
if (!$conn) {
echo "connect failed";
exit;
}
mysql_select_db("big", $conn);
mysql_query("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','$type')";
mysql_query($sql, $conn);
}
//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')";
$order_rs = mysql_query($sql, $conn);
//库存减少
$sql = "update ih_store set number=number-{$number} where sku_id='$sku_id'";
$store_rs = mysql_query($sql, $conn);
if (mysql_affected_rows()) {
insertLog('库存减少成功');
} else {
insertLog('库存减少失败');
}
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。
我之间做商城项目的时候,在秒杀这一块我直接用的redis,这段时间看了看上面的几种方法,虽然各有不同,但是实现目的都一样的,各位自己选择,开心就好。
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