Windows – CPU under heavy load with simple file copy on windows VPS on ESXi host

For PHP there are 2 important things that will increase capacity:

1. Advanced PHP Caching (APC) as was mentioned. This is what we use at Yahoo!. There are other similar projects, but this one is Rasmus' baby.
2. FastCGI instead of mod_php. There is debate on this issue as mod_php is usually the fastest. However, I would assume that you have a single Apache server delivering both dynamic PHP content and static assets (JS, CSS, flash, images, PDFs, etc.). The requests for those static assets do not need to consume as much memory, but because PHP is a module it is in every Apache thread.

For Apache:

1. Use worker MPM
2. Enable KeepAlive

You may also go so far as to consider switching from Apache to Lighttpd, or Nginx. I love Apache. I use the fool out of many of it's advanced features. I accept its overhead because I need what it offers. For the common LAMP stack, it is more than is needed and a waste of resources.

For MySQL:

1. Your optimization efforts will payoff 10 fold when spent analyzing and correcting queries, instead of tweaking your my.cnf values. I'm not saying that it's not important to get your caching, connections, etc. correct... but for most people it is only 9% of the problem.
2. During your QA, turn on the general query log on your staging/dev mysqld to capture all queries sent. (Do NOT do that on your production mysql server!)
3. Use EXPLAIN to analyze the queries. Especially if you are using a framework with an ORM (abstracts away the DB and keeps you from writing your own SQL) you will need to clean out extraneous JOINs, SELECTs with no WHERE clause, ORDER BYs that induce 'using filesort', and queries that use no indexes.
4. If you are using MySQL 5.1 take advantage of the query profiler.

Other tools worth considering are mk-visual-explain

I've cited 10 great references. These things ought to get you humming. Please lets us know how it turns out.

First, you really should ask yourself the question: Is 250 req / second something your site really should be able to handle? That is a LOT of requests for a page. Quite frankly, I think 250req/s maxing your CPU is normal given what you have -- a virtualized system.

pm.max_children = 150

You probably kept on raising this because you keep on getting error saying you're maxed out on children. But you're actually shooting yourself in the foot when you raise this beyond what your system can handle. It's better to NOT accept a next request it can't handle than to accept. Increasing this not only thins out your system, you create more resource requirements as well as more overhead. And when that explodes to a size your system can no longer handle, it creates signs like freezing. I don't know exactly what your VPS is giving you (and you'll never know since it's not static as it depends on other users in the node), but I would personally say that anything above 20 for your specified system is a not realistic setting.

You should also adjust start/min/max spare accordingly as having then greater than max children makes no sense. Or you can just not worry about it and set to pm = static.