Adjusting the PHP Setting pm.max_children

Introduction

The PHP setting pm.max_children defines the maximum number of PHP child processes that can be active at the same time. If your website has a high number of users, multiple PHP-FPM processes must be running to handle the requests. This setting ensures that the number of concurrently running processes is monitored and optimized to prevent the server from becoming overloaded, for example, due to high user traffic.

To adjust the PHP setting pm.max_children, first log in to our Customer Center at account.creoline.com using your login credentials.

Use the navigation menu to select the server under Server for which you want to change the PHP settings. Then open the Plesk Control Panel via the Plesk Control Panel menu item.

Customizing Settings for a Single Domain

Once you’re logged in to Plesk, you can select the domain using the global search or the Websites & Domains menu item.

Using the PHP Settings button, you can adjust the general PHP settings and the PHP setting pm.max_children.

The pm.max_children value defines the maximum number of concurrent PHP processes. This value can be set freely and is specified in the unit “number.”

Calculating pm.max_children (Maximum)

The maximum possible value for pm.max_children can be calculated using the following formula:

(RAM - 2 GiB) / Memory Limit = Maximum value for pm.max_children
 ^ ^ ^ 
 | | |
      | | |
 | | └ Defined PHP memory limit value
 | └ Memory reserved for other services (value may vary)
 └ Total server memory

Calculating pm.max_children (Recommended)

We recommend calculating the number of pm.max_children using the following formula:

(RAM - 2 GiB) / PHP process size = Recommended value for pm.max_children
      ^ ^ ^ 
 | | |
 | | |
 | | └ Average PHP process size
 | └ Memory reserved for other services (value may vary)
 └ Total server RAM

The average PHP process size can be determined, for example, using a PHP profiler. We recommend using Tideways for PHP profiling. A Tideways license can be purchased directly through our support team; see also: Price List for Additional and Special Services.

Once the settings have been saved, the web server automatically reloads the configuration using a graceful restart, so that existing requests are not terminated but rather paused.

Example Calculation for pm.max_children

# Calculating the available memory for PHP
16,384 MiB - 6,144 MiB = 10,240 MiB

# Calculating the recommended value for pm.max_children
10,240 MiB / 100 MiB = ~102 pm.max_children

Additional Configuration Options

The PHP settings also allow you to adjust pm.max_requests, the desired pm process manager, or pm.start_servers, pm.min_spare_servers, and pm.max_spare_servers.