Adjust PHP setting pm.max_children

Preface

The PHP setting pm.max_children defines the maximum number of PHP child processes available at the same time. If your website has a high number of users, several PHP-FPM processes must be executed to process the requests. The setting ensures that the number of simultaneously executed processes is monitored and optimized so that the server is not overloaded by a high number of users, for example.

To adjust the PHP setting pm.max_children, first log in to our customer center at account.creoline.com with your access data.

Use the navigation to select your 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.

Customization for a single domain

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

You can use the PHP settings button to adjust the general PHP settings and the PHP setting pm.max_children.

The value pm.max_children defines the maximum number of concurrent PHP processes. This value is freely definable and is specified in the unit number.

Calculation 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
      | Reserved working memory for other services (value may vary)
      Working memory of the entire server

Calculation pm.max_children (Recommended)

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

(memory - 2 GiB) / PHP process size = Recommended value for pm.max_children
      ^ ^ ^
      | | |
      | | |
      | | | └ Average PHP process size
      | Reserved working memory for other services (value may vary)
      Working memory of the entire server

The average PHP process size can be determined using a PHP profiler, for example. We recommend using Tideways for PHP profiling. A Tideways license can be purchased directly from our support team, see also: Price list for additional services and special services

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

Example calculation pm.max_children

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

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

Further setting options

Under the PHP settings, it is also possible to adjust the pm.max_requests, the desired pm process manager or the pm.start_servers, pm.min_spare_servers and the pm.max_spare_servers.