使用redis防止商品超发

• redis不仅仅是单纯的缓存，它还有一些特殊的功能，在一些特殊场景上很好用。redis中key的原子自增incrby和判断key不存在再写入的setnx方法，可以有效的防止超发。
• 下面使用两个不同的方式来说明利用redis做商品购买库存数量限制。
• 业务场景很简单，就是限制抢购5个商品，模拟并发请求抢购商品，每抢购一次对应redis中的key值增加一次，通过判断限购的数量来限制抢购，抢购成功写入成功日志，失败写入失败的信息记录，通过记录的数量来判断是否超发。

文件index.php

<?php
require_once './myRedis.php';
require_once './function.php';

class sendAward{
	public $conf = [];
	const V1 = 'way1';//版本一
	const V2 = 'way2';//版本二
	const AMOUNTLIMIT = 5;//抢购数量限制
	const INCRAMOUNT = 1;//redis递增数量值

	//初始化调用对应方法执行商品发放
	public function __construct($conf,$type){
		$this->conf = $conf;
		if(empty($type))
			return '';
		if($type==self::V1){
			$this->way1(self::V1);
		}elseif($type==self::V2){
			$this->way2(self::V2);
		}else{
			return '';
		}
	}

	//抢购商品方式一
	protected  function way1($v){
		$redis = new myRedis($this->conf);
		$keyNmae = getKeyName($v);
		if(!$redis->exists($keyNmae)){
			$redis->set($keyNmae,0);
		}
		$currAmount = $redis->get($keyNmae);
		if(($currAmount+self::INCRAMOUNT)>self::AMOUNTLIMIT){
			writeLog("没有抢到商品",$v);
			return;
		}
		$redis->incrby($keyNmae,self::INCRAMOUNT);
		writeLog("抢到商品",$v);
	}

	//抢购商品方式二
	protected function way2($v){
		$redis = new myRedis($this->conf);
		$keyNmae = getKeyName($v);
		if(!$redis->exists($keyNmae)){
			$redis->setnx($keyNmae,0);
		}
		if($redis->incrby($keyNmae,self::INCRAMOUNT) > self::AMOUNTLIMIT){
			writeLog("没有抢到商品",$v);
			return;
		}
		writeLog("抢到商品",$v);
	}

}

//实例化调用对应执行方法
$type = isset($_GET['v'])?$_GET['v']:'way1';
$conf = [
	'host'=>'192.168.0.214','port'=>'6379',
	'auth'=>'test','db'=>2,
];
new sendAward($conf,$type);

文件myRedis.php

<?php
/**
 * @desc 自定义redis操作类
 * **/
class myRedis{
	public $handler = NULL;
	public function __construct($conf){
		$this->handler = new Redis();
		$this->handler->connect($conf['host'], $conf['port']); //连接Redis
		//设置密码
		if(isset($conf['auth'])){
			$this->handler->auth($conf['auth']); //密码验证
		}
		//选择数据库
		if(isset($conf['db'])){
			$this->handler->select($conf['db']);//选择数据库2
		}else{
			$this->handler->select(0);//默认选择0库
		}
	}

	//获取key的值
	public function get($name){
		return $this->handler->get($name);
	}

	//设置key的值
	public function set($name,$value){
		return $this->handler->set($name,$value);
	}

	//判断key是否存在
	public function exists($key){
		if($this->handler->exists($key)){
			return true;
		}
		return false;
	}

	//当key不存在的设置key的值，存在则不设置
	public function setnx($key,$value){
		return $this->handler->setnx($key,$value);
	}

	//将key的数值增加指定数值
	public function incrby($key,$value){
		return $this->handler->incrBy($key,$value);
	}

}

文件function.php

<?php
//获取商品key名称
function getKeyName($v)
{
	return "send_goods_".$v;
}

//日志写入方法
function writeLog($msg,$v)
{
	$log = $msg.PHP_EOL;
	file_put_contents("log/$v.log",$log,FILE_APPEND);
}

1.ab工具并发测试way1方法

[root@localhost oversend]# ab -c 100 -n 200 http://192.168.0.213:8083/index.php?v=way1
This is ApacheBench, Version 2.3 <$Revision: 655654 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking 192.168.0.213 (be patient)
Completed 100 requests
Completed 200 requests
Finished 200 requests

Server Software:        nginx
Server Hostname:        192.168.0.213
Server Port:            8083

Document Path:          /index.php?v=way1
Document Length:        0 bytes

Concurrency Level:      100
Time taken for tests:   0.089 seconds
Complete requests:      200
Failed requests:        0
Write errors:           0
Total transferred:      30600 bytes
HTML transferred:       0 bytes
Requests per second:    2243.13 [#/sec] (mean)
Time per request:       44.581 [ms] (mean)
Time per request:       0.446 [ms] (mean, across all concurrent requests)
Transfer rate:          335.16 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    6   2.2      5      17
Processing:     2   28  16.3     25      55
Waiting:        1   26  15.2     24      50
Total:          5   34  16.3     30      60

Percentage of the requests served within a certain time (ms)
  50%     30
  66%     35
  75%     54
  80%     56
  90%     57
  95%     60
  98%     60
  99%     60
 100%     60 (longest request)

v1方法日志分析

[root@localhost log]# less -N way1.log
      1 抢到商品
      2 抢到商品
      3 抢到商品
      4 抢到商品
      5 抢到商品
      6 抢到商品
      7 没有抢到商品
      8 没有抢到商品
      9 没有抢到商品
     10 没有抢到商品
     11 没有抢到商品
     12 没有抢到商品

观察日志发现 抢到商品的记录有6条超过正常的5条，说明超发了

2.ab工具并发测试way2方法

[root@localhost oversend]# ab -c 100 -n 200 http://192.168.0.213:8083/index.php?v=way2
This is ApacheBench, Version 2.3 <$Revision: 655654 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking 192.168.0.213 (be patient)
Completed 100 requests
Completed 200 requests
Finished 200 requests

Server Software:        nginx
Server Hostname:        192.168.0.213
Server Port:            8083

Document Path:          /index.php?v=way2
Document Length:        0 bytes

Concurrency Level:      100
Time taken for tests:   0.087 seconds
Complete requests:      200
Failed requests:        0
Write errors:           0
Total transferred:      31059 bytes
HTML transferred:       0 bytes
Requests per second:    2311.68 [#/sec] (mean)
Time per request:       43.259 [ms] (mean)
Time per request:       0.433 [ms] (mean, across all concurrent requests)
Transfer rate:          350.58 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    6   5.4      5      13
Processing:     3   31  16.6     30      70
Waiting:        1   30  16.6     30      70
Total:          5   37  18.5     32      82

Percentage of the requests served within a certain time (ms)
  50%     32
  66%     41
  75%     45
  80%     50
  90%     68
  95%     80
  98%     81
  99%     82
 100%     82 (longest request)

v2方法日志分析

[root@localhost log]# less -N v2.log
[root@localhost log]# less -N way2.log
      1 抢到商品
      2 抢到商品
      3 抢到商品
      4 抢到商品
      5 没有抢到商品
      6 抢到商品
      7 没有抢到商品
      8 没有抢到商品
      9 没有抢到商品
     10 没有抢到商品

总结：观察日志可知抢到商品的日志记录是5条并没有超发，说明利用这种方式可以限制住库存的数量。之所以超发是因为方法一中通过加法来判断限制条件的同时，并发一大，就会越过这个判断条件出现会超发，redis的在这方面就体现优势了。

完整代码github地址