w3wp.exe runs out of memory even though there's still memory available

Question

We're running into a strange problem. Our ASP.NET application is running on 64-bit Windows 2008/IIS7 machine with 16Gb of RAM. When w3wp.exe process reaches 4Gb (we track it simple via Task Manager on the server) - Out of Memory exeption is thrown even though there's a plenty of memory still available.

Is there a known issue were ASP.NET process is limited to 4Gb of memory on 64bit system (and using 64bit app pool)?

Is there any way to lift that limit?

Answer 1

It kind of sounds like you have an undisposed resource somewhere that ends up getting garbage collected eventually, but not quickly enough for your needs. Do you reuse any SQLConnection objects? Or MailClient objects? Or unmanaged Image objects?

As for the lower-than-expected memory limit, there are two types of memory use by a ASP.NET app. One is reserved memory and the other is actually used memory. I believe the task manager tracks actual memory use, but reserved memory probably also has a limit. To find out how much reserved memory your process is taking up, go to IIS7, click on the server (the top level, above app pools and sites folder), then click the Processes option and then click your app's process. It should show you CPU use, number of requests and memory usage (both reserved and actual).