IIS and the number of w3wp processes

Question

I'm running IIS 7 on Server 2008, with a single AppPool for an application which is basically just a collection of ASP.NET WebMethods. Some of these methods process for hours before they return.

What's weird, is that sometimes when I launch multiple simultaneous requests IIS spins up a single w3wp process (and seems to share it amongst the requests) and other times it spins up multiple w3wp processes (1 for each request).

I am always careful to use task mgr and view processes for all users when observing this. Can anyone explain this inconsistent behavior?

Answer 1

It may be time to re-think your web-garden. Scott Forsyth has an interesting 11 minute vLog on why webgardens are counterproductive: http://dotnetslackers.com/articles/iis/Why-You-Shouldnt-Use-Web-Gardens-in-IIS-Week-24.aspx

Links to articles he mentions in his VLog:

Tuning recommendations for IIS6 and IIS7 -- read the whole article: http://support.microsoft.com/kb/821268 Further information http://blogs.msdn.com/b/tmarq/archive/2007/07/21/asp-net-thread-usage-on-iis-7-0-and-6-0.aspx

His bottom line is if you have performance problems that are resolved by web gardens—use the web gardens as a great crutch until the underlying performance issue (usually resource contention) is resolved.

Answer 2

By default each app pool gets 1 w3wp process, but in a web garden multiple w3wp processes can exist per app pool.

Edit: A little more info about web gardens