发出并发请求时，php curl localhost很慢答案

【问题标题】：php curl localhost is slow when making concurrent requests发出并发请求时，php curl localhost很慢
【发布时间】：2017-01-29 14:40:06
【问题描述】：

我有一个有趣的问题，我不确定根本原因是什么。我有一个服务器和两个虚拟主机 A 和 B，端口分别在 80 和 81 上运行。我在 A 上编写了一个简单的 PHP 代码，如下所示：

<?php

echo "from A server\n";

B 上还有一个简单的 PHP 代码：

<?php

echo "B server:\n";

// create curl resource 
$ch = curl_init(); 

// set url 
curl_setopt($ch, CURLOPT_URL, "localhost:81/a.php"); 

//return the transfer as a string 
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1); 

// $output contains the output string 
$output = curl_exec($ch); 

// close curl resource to free up system resources 
curl_close($ch);

echo $output;

当使用ab 发出并发请求时，我得到以下结果：

ab -n 10 -c 5 http://192.168.10.173/b.php
This is ApacheBench, Version 2.3 <$Revision: 1706008 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking 192.168.10.173 (be patient).....done


Server Software:        nginx/1.10.0
Server Hostname:        192.168.10.173
Server Port:            80

Document Path:          /b.php
Document Length:        26 bytes

Concurrency Level:      5
Time taken for tests:   2.680 seconds
Complete requests:      10
Failed requests:        0
Total transferred:      1720 bytes
HTML transferred:       260 bytes
Requests per second:    3.73 [#/sec] (mean)
Time per request:       1340.197 [ms] (mean)
Time per request:       268.039 [ms] (mean, across all concurrent requests)
Transfer rate:          0.63 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    0   0.1      0       1
Processing:     2 1339 1408.8   2676    2676
Waiting:        2 1339 1408.6   2676    2676
Total:          3 1340 1408.8   2676    2677

Percentage of the requests served within a certain time (ms)
  50%   2676
  66%   2676
  75%   2676
  80%   2676
  90%   2677
  95%   2677
  98%   2677
  99%   2677
 100%   2677 (longest request)

但是以并发级别 1 发出 1000 个请求非常快：

$ ab -n 1000 -c 1 http://192.168.10.173/b.php
This is ApacheBench, Version 2.3 <$Revision: 1706008 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking 192.168.10.173 (be patient)
Completed 100 requests
Completed 200 requests
Completed 300 requests
Completed 400 requests
Completed 500 requests
Completed 600 requests
Completed 700 requests
Completed 800 requests
Completed 900 requests
Completed 1000 requests
Finished 1000 requests


Server Software:        nginx/1.10.0
Server Hostname:        192.168.10.173
Server Port:            80

Document Path:          /b.php
Document Length:        26 bytes

Concurrency Level:      1
Time taken for tests:   1.659 seconds
Complete requests:      1000
Failed requests:        0
Total transferred:      172000 bytes
HTML transferred:       26000 bytes
Requests per second:    602.86 [#/sec] (mean)
Time per request:       1.659 [ms] (mean)
Time per request:       1.659 [ms] (mean, across all concurrent requests)
Transfer rate:          101.26 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    0   0.1      0       1
Processing:     1    1  10.3      1     201
Waiting:        1    1  10.3      1     201
Total:          1    2  10.3      1     201

Percentage of the requests served within a certain time (ms)
  50%      1
  66%      1
  75%      1
  80%      1
  90%      1
  95%      1
  98%      1
  99%      2
 100%    201 (longest request)

谁能解释为什么会这样？我真的很想知道根本原因。这是卷曲的问题吗？感觉不像是网络瓶颈或打开文件问题，因为并发只有 5。顺便说一句，我也尝试使用 guzzlehttp 做同样的事情，但结果是一样的。我在笔记本电脑上使用 ab 并且服务器位于同一个本地网络中。另外，它当然与网络带宽无关，因为主机 A 和 B 之间的请求是在 localhost 完成的。

我已经修改了代码，让测试更加灵活：

<?php

require 'vendor/autoload.php';

use GuzzleHttp\Client;

$opt = 1;
$url = 'http://localhost:81/a.php';

switch ($opt) {
    case 1:
        // create curl resource
        $ch = curl_init();

        // set url
        curl_setopt($ch, CURLOPT_URL, $url);

        //return the transfer as a string
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);

        // $output contains the output string
        $output = curl_exec($ch);

        curl_close($ch);

        echo $output;
        break;
    case 2:
        $client = new Client();
        $response = $client->request('GET', $url);
        echo $response->getBody();
        break;
    case 3:
        echo file_get_contents($url);
        break;
    default:
        echo "no opt";
}

echo "app server:\n";

我尝试了file_get_contents，但是切换到file_get_contents时没有明显的区别。当并发为 1 时，所有方法都很好。但是当并发增加时，它们都开始降级。

我想我找到了与这个问题相关的东西，所以我只发布了另一个问题concurrent curl could not resolve host。这可能是根本原因，但我还没有任何答案。

尝试了这么久，我认为这肯定与名称解析有关。这是可以在并发级别 500 执行的 php 脚本

<?php

require 'vendor/autoload.php';

use GuzzleHttp\Client;

$opt = 1;
$url = 'http://localhost:81/a.php';

switch ($opt) {
    case 1:
        // create curl resource
        $ch = curl_init();

        // set url
        curl_setopt($ch, CURLOPT_URL, $url);

        //return the transfer as a string
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);

        curl_setopt($ch, CURLOPT_PROXY, 'localhost');

        // $output contains the output string
        $output = curl_exec($ch);

        curl_close($ch);

        echo $output;
        break;
    case 2:
        $client = new Client();
        $response = $client->request('GET', $url, ['proxy' => 'localhost']);
        echo $response->getBody();
        break;
    case 3:
        echo file_get_contents($url);
        break;
    default:
        echo "no opt";
}

echo "app server:\n";

真正重要的是curl_setopt($ch, CURLOPT_PROXY, 'localhost'); 和$response = $client->request('GET', $url, ['proxy' => 'localhost']);。它告诉 curl 使用 localhost 作为代理。

这是ab测试的结果

ab -n 1000 -c 500 http://192.168.10.173/b.php
This is ApacheBench, Version 2.3 <$Revision: 1528965 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking 192.168.10.173 (be patient)
Completed 100 requests
Completed 200 requests
Completed 300 requests
Completed 400 requests
Completed 500 requests
Completed 600 requests
Completed 700 requests
Completed 800 requests
Completed 900 requests
Completed 1000 requests
Finished 1000 requests


Server Software:        nginx/1.10.0
Server Hostname:        192.168.10.173
Server Port:            80

Document Path:          /b.php
Document Length:        182 bytes

Concurrency Level:      500
Time taken for tests:   0.251 seconds
Complete requests:      1000
Failed requests:        184
   (Connect: 0, Receive: 0, Length: 184, Exceptions: 0)
Non-2xx responses:      816
Total transferred:      308960 bytes
HTML transferred:       150720 bytes
Requests per second:    3985.59 [#/sec] (mean)
Time per request:       125.452 [ms] (mean)
Time per request:       0.251 [ms] (mean, across all concurrent requests)
Transfer rate:          1202.53 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    6   4.9      5      14
Processing:     9   38  42.8     22     212
Waiting:        8   38  42.9     22     212
Total:         11   44  44.4     31     214

Percentage of the requests served within a certain time (ms)
  50%     31
  66%     37
  75%     37
  80%     38
  90%    122
  95%    135
  98%    207
  99%    211
 100%    214 (longest request)

但是为什么在不使用 localhost 作为代理时，名称解析在并发级别 5 时仍然失败？

虚拟主机设置非常简单干净，几乎所有东西都是默认配置。我没有在这台服务器上使用 iptables，也没有配置任何特别的东西。

server {
    listen 81 default_server;
    listen [::]:81 default_server;

    root /var/www/html;

    index index.html index.htm index.nginx-debian.html;

    server_name _;

    location / {
        try_files $uri $uri/ =404;
    }

    location ~ \.php$ {
        include snippets/fastcgi-php.conf;
        fastcgi_pass unix:/run/php/php7.0-fpm.sock;
    }
}

发现一些有趣的东西！如果您在第一次之后在大约 3 秒内立即进行另一次 ab 测试。第二个ab测试很快。

不使用本地主机作为代理

ab -n 10 -c 5 http://192.168.10.173/b.php <-- This takes 2.8 seconds to finish.
ab -n 10 -c 5 http://192.168.10.173/b.php <-- This takes 0.008 seconds only.

使用 localhost 作为代理

ab -n 10 -c 5 http://192.168.10.173/b.php <-- This takes 0.006 seconds.
ab -n 10 -c 5 http://192.168.10.173/b.php <-- This takes 0.006 seconds.

我认为这仍然意味着问题是名称解析。但为什么呢？

假设：nginx 没有监听 localhost:81

我尝试将listen 127.0.0.1:81;添加到nginx，它显示没有效果。

发现自己在使用 curl 代理时犯了一些错误，这不起作用！稍后更新其他细节。

已解决，与代理无关，或任何事情。根本原因是php-fpm的www.conf中的pm.start_servers。

【问题讨论】：

如果您使用不同的并发级别（如 2）或 URL fopen() （如 file_get_contents("localhost:81/a.php");) ），这种情况是否会发生根本变化？
@BJBlack at concurrcy = 2,3,4,5，时间分别为0.018s、0.87s、1.75s、2.42s。我怀疑这与低级 linux 行为有关。
@cwhsu 在这种情况下，您可能希望将 linux 作为标签压缩
@Goose 好的，完成！我仍然对这个问题感到困惑。
检查会话自动启动等内容。如果您有默认的基于文件的会话，则不可能为并发请求提供服务，因为“活动”脚本会锁定会话文件，从而阻止任何其他并行请求。

标签： php linux curl concurrency localhost

【解决方案1】：

好的，经过这么多天的尝试解决这个问题，我终于找到了原因。这不是名称解析。我不敢相信需要这么多天才能找到根本原因，即 php-fpm 的www.conf 中的pm.start_servers 的数量。最初，我将 pm.start_servers 的数量设置为 3，这就是为什么对 localhost 的 ab 测试总是在 并发级别 3 之后变得更糟。虽然 php-cli 没有 php 进程数量有限的问题，但 php-cli 总是表现出色。将pm.start_servers增加到5后，ab测试结果和php-cli一样快。如果这是您的 php-fpm 速度慢的原因，您还应该考虑更改 pm.min_spare_servers、pm.max_spare_servers、pm.max_children 的数量以及任何相关内容。

【讨论】：