What does PHP-FPM do?
PHP FastCGI Process Manager (PHP-FPM) is an alternative FastCGI daemon for PHP that allows a website to handle strenuous loads. It also allows for a host to set specific amounts of resources to process a domain’s requests. PHP-FPM maintains “pools” (workers available to respond to PHP requests) to accomplish this. These “pools” of workers allow the website to handle more requests than it normally could.
PHP-FPM is faster than traditional CGI-based methods, such as SUPHP, for multi-user PHP environments. It does not overload a system’s memory with PHP from Apache processes like
ruid2+php-dso does. This method is useful when a user receives extra traffic that requires resources to process it. For example, your website may receive a spike in traffic after a TV show features it or is linked from a popular website.
You can examine your server, locate the source of the extra traffic, and then enable PHP-FPM on that site via the pool manager. PHP-FPM does this through a service to serve PHP requests that Apache routes traffic to. PHP-FPM only executes PHP requests, which enables it to service content quicker than other methods.
Source: Read more about PHP-FPM