Apache run PHP

Module in Apache

This means that when the same client makes a second request to the server,
 it may be served by a different child process than the first time.
When opening a persistent connection,
 every following page requesting SQL services can reuse the same established connection to the SQL server.

CGI "wrapper"

persistent connections don't persist. (cgi 每行一次就會死亡)

fastCGI

In this case, PHP processes are NOT destroyed after each request, and so persistent connections do persistn

plug-in for a multithreaded web server (WSAPI, and NSAPI (on Windows))

The behavior is essentially the same as "Module in Apache"