IIS memory leak detection techniques

I have a server running about 100+ WordPress sites of varying complexity and traffic volume. The OS is Windows 2003 Server 开发者_如何学Gorunning IIS 6 with the domains being managed via HELM. The thing is there are times when sites stop responding due to insufficient memory, but it has been difficult to track the particular site(s) or other culprit that could be the cause. What makes it even more complicated is that the problem will disappear for weeks and then show up again. The most recent solution was to migrate the sites to a higher capacity server and this seemed to have worked for some time.

What tools/techniques can I use to track down the problem while keeping in mind that this is a production server?

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Tess Ferrandez has a number of great articles about tracking down memory pressure and process hangs in IIS using WinDbg and DebugDiag:

If it is broken, fix it you should

Whilst the techniques often focus on ASP.NET, many of the techniques can be applied to other languages. The only problem is that because PHP is written using native code your WinDbg-fu will probably need to be fairly good.