# Apache vs. PHP-FPM Bottleneck with Child Processes

https://hostcarts.qa/knowledgebase/article/apache-vs-php-fpm-bottleneck-with-child-processes

## Overview

Apache servers that use the `prefork` MPM with fewer server instances than the maximum number of PHP-FPM child processes may experience performance issues. This document explains how to resolve these dependency issues.

Important:

This issue and solution **only** apply to servers that run Apache’s `prefork` MPM.

## The issue

In the following scenario, the PHP-FPM server’s configuration allows a maximum of 20 PHP-FPM child processes and the Apache server’s configuration allows five server instances.

The following example represents the PHP-FPM server’s configuration file:

| `1 2 3` | `_is_present: 1 pm_max_children: 20 pm_max_requests: 20` |
| --- | --- |

The following example represents the Apache server’s configuration file:

| `1 2 3 4 5` | `StartServers: 5 <IfModule prefork.c> MinSpareServers: 10 MaxSpareServers: 10 </IfModule>` |
| --- | --- |

If the Apache server receives 20 requests, it immediately passes ten of those requests to the available PHP-FPM child processes. After PHP-FPM processes those requests, Apache will pass another ten requests to PHP-FPM.

Warning:

For high-volume servers, this configuration can cause severe performance issues.

## The solution

To solve this issue, you **must** configure Apache to allow enough server instances to handle the maximum number of PHP-FPM child processes. To do this, configure the following options in WHM’s [*Global Configuration*](https://docs.cpanel.net/whm/service-configuration/global-configuration) interface (*WHM >> Home >> Service Configuration >> Global Configuration*):

- *Minimum Spare Servers*
- *Maximum Spare Servers*
- *Max Request Workers*

Set these options to a value greater than or equal to the `pm_max_children` setting in the PHP-FPM server’s configuration file.