This only applies to VMs running Plesk 12 or newer, and have PHP set to run as an FPM application. This is specified in Plesk under:
Domains > domainname > PHP Settings
PHP-FPM is generally quicker and less resource-intensive as running in fast\fcgi mode. However if you wish to change the default limits Plesk sets on PHP-FPM sites then you need to create a custom php.ini file for any domains you want to change the limits to.
This is done by creating a blank file named php.ini in the following location:
where mydomain.tld is the name of the domain whose settings you wish to change.
Then to have plesk read in your changes run the following command via SSH:
For example if you wanted to change the max_children limit you would put the following in to this file:
pm.max_children = 20
A limit of 20 should be safe enough for our Business VMs or higher with a handful of busy sites, or a larger number of smaller websites.