Php – Windows / Apache / PHP CPU at 100% under small load

Tracking down WHAT is causing the problem can be a pain in the ass. The first thing I'd do if I had a problem like that is reduce MaxRequestsPerChild to an aggresively low number (~100-200) and see if that makes a difference. If it does, then you probably have code that is leaking memory in a loop somewhere and you'll want to run a code audit.

Another thing to look at is Apache's fullstatus, see if you can find out what particular request is causing the memory leak. Get the PIDs on your suspected processes and run an strace on them.

Running PHP via FastCGI will certainly give you the most flexibility. Not only can you safely use an mpm-worker Apache, you can even use another webserver altogether (e.g. nginx).

But even when staying with Apache, "PHP via FastCGI" is at the moment not one option, but at least two: mod_fastcgi, mod_fcgid. On top of that, you can either use dynamic, static, or external FastCGI processes; with or without suexec. And then there's PHP's internal FastCGI process manager, which is now replaced by the very nice PHP-FPM in PHP 5.3. All those options have different pros and cons and can lead to different problems.

Given the choice, I would pick mod_fastcgi with PHP-FPM at the moment, mostly because it allows for extremely versatile and stable setups.