- redis不僅僅是單純的緩存，它還有一些特殊的功能，在一些特殊場景上很好用。redis中key的原子自增incrby和判斷key不存在再寫入的setnx方法，可以有效的防止超發。
- 下面使用兩個不同的方式來說明利用redis做商品購買庫存數量限制。
- 業務場景很簡單，就是限制搶購5個商品，模擬並發請求搶購商品，每搶購一次對應redis中的key值增加一次，通過判斷限購的數量來限制搶購，搶購成功寫入成功日志，失敗寫入失敗的信息記錄，通過記錄的數量來判斷是否超發。
文件index.php
<?php
require_once './myRedis.php';
require_once './function.php';
class sendAward{
public $conf = [];
const V1 = 'way1';//版本一
const V2 = 'way2';//版本二
const AMOUNTLIMIT = 5;//搶購數量限制
const INCRAMOUNT = 1;//redis遞增數量值
//初始化調用對應方法執行商品發放
public function __construct($conf,$type){
$this->conf = $conf;
if(empty($type))
return '';
if($type==self::V1){
$this->way1(self::V1);
}elseif($type==self::V2){
$this->way2(self::V2);
}else{
return '';
}
}
//搶購商品方式一
protected function way1($v){
$redis = new myRedis($this->conf);
$keyNmae = getKeyName($v);
if(!$redis->exists($keyNmae)){
$redis->set($keyNmae,0);
}
$currAmount = $redis->get($keyNmae);
if(($currAmount+self::INCRAMOUNT)>self::AMOUNTLIMIT){
writeLog("沒有搶到商品",$v);
return;
}
$redis->incrby($keyNmae,self::INCRAMOUNT);
writeLog("搶到商品",$v);
}
//搶購商品方式二
protected function way2($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("沒有搶到商品",$v);
return;
}
writeLog("搶到商品",$v);
}
}
//實例化調用對應執行方法
$type = isset($_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 自定義redis操作類
* **/
class myRedis{
public $handler = NULL;
public function __construct($conf){
$this->handler = new Redis();
$this->handler->connect($conf['host'], $conf['port']); //連接Redis
//設置密碼
if(isset($conf['auth'])){
$this->handler->auth($conf['auth']); //密碼驗證
}
//選擇數據庫
if(isset($conf['db'])){
$this->handler->select($conf['db']);//選擇數據庫2
}else{
$this->handler->select(0);//默認選擇0庫
}
}
//獲取key的值
public function get($name){
return $this->handler->get($name);
}
//設置key的值
public function set($name,$value){
return $this->handler->set($name,$value);
}
//判斷key是否存在
public function exists($key){
if($this->handler->exists($key)){
return true;
}
return false;
}
//當key不存在的設置key的值，存在則不設置
public function setnx($key,$value){
return $this->handler->setnx($key,$value);
}
//將key的數值增加指定數值
public function incrby($key,$value){
return $this->handler->incrBy($key,$value);
}
}
文件function.php
<?php
//獲取商品key名稱
function getKeyName($v)
{
return "send_goods_".$v;
}
//日志寫入方法
function writeLog($msg,$v)
{
$log = $msg.PHP_EOL;
file_put_contents("log/$v.log",$log,FILE_APPEND);
}
1.ab工具並發測試way1方法
[root@localhost oversend]# ab -c 100 -n 200 http://192.168.0.213:8083/index.php?v=way1
This is ApacheBench, Version 2.3 <$Revision: 655654 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/
Benchmarking 192.168.0.213 (be patient)
Completed 100 requests
Completed 200 requests
Finished 200 requests
Server Software: nginx
Server Hostname: 192.168.0.213
Server Port: 8083
Document Path: /index.php?v=way1
Document Length: 0 bytes
Concurrency Level: 100
Time taken for tests: 0.089 seconds
Complete requests: 200
Failed requests: 0
Write errors: 0
Total transferred: 30600 bytes
HTML transferred: 0 bytes
Requests per second: 2243.13 [#/sec] (mean)
Time per request: 44.581 [ms] (mean)
Time per request: 0.446 [ms] (mean, across all concurrent requests)
Transfer rate: 335.16 [Kbytes/sec] received
Connection Times (ms)
min mean[+/-sd] median max
Connect: 0 6 2.2 5 17
Processing: 2 28 16.3 25 55
Waiting: 1 26 15.2 24 50
Total: 5 34 16.3 30 60
Percentage of the requests served within a certain time (ms)
50% 30
66% 35
75% 54
80% 56
90% 57
95% 60
98% 60
99% 60
100% 60 (longest request)
v1方法日志分析
[root@localhost log]# less -N way1.log
1 搶到商品
2 搶到商品
3 搶到商品
4 搶到商品
5 搶到商品
6 搶到商品
7 沒有搶到商品
8 沒有搶到商品
9 沒有搶到商品
10 沒有搶到商品
11 沒有搶到商品
12 沒有搶到商品
觀察日志發現 搶到商品的記錄有6條超過正常的5條，說明超發了
2.ab工具並發測試way2方法
[root@localhost oversend]# ab -c 100 -n 200 http://192.168.0.213:8083/index.php?v=way2
This is ApacheBench, Version 2.3 <$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 搶到商品
2 搶到商品
3 搶到商品
4 搶到商品
5 沒有搶到商品
6 搶到商品
7 沒有搶到商品
8 沒有搶到商品
9 沒有搶到商品
10 沒有搶到商品
總結：觀察日志可知搶到商品的日志記錄是5條並沒有超發，說明利用這種方式可以限制住庫存的數量。之所以超發是因為方法一中通過加法來判斷限制條件的同時，並發一大，就會越過這個判斷條件出現會超發，redis的在這方面就體現優勢了。