Glossary

PHP-FPM

PHP-FPM (FastCGI Process Manager) is a PHP process manager that maintains a pool of workers for handling PHP requests. Nginx or Apache forward requests to PHP-FPM via FastCGI; it executes the script and returns a response.

Pools and workers

PHP-FPM starts N child processes (workers). Each worker handles one request at a time. Three pool management modes:

static — fixed number of workers
dynamic — count between min and max based on load
ondemand — workers start on request and stop after idle time

Key parameters

pm.max_children — maximum concurrent requests. Formula: RAM / (~30 MB per worker)
request_terminate_timeout — kill a worker if a request runs longer than N seconds
pm.max_requests — restart a worker after N requests (prevents memory leaks)