asp.net - High memory usage with w3wp application pool IIS 7

Question

I have a website application running in it's own application pool on IIS 7.0. The application is an ASP.NET MVC 3 website.

I have noticed the memory usage for this applications corresponding w3wp IIS worker service is quite high ( 800 MB, with some fluctuation ).

I am trying to diagnose the problem and have tried the following:

I have disabled output page caching for the website at IIS level and then recycled the application pool. This causes the w3wp process to restart. The memory usage for this process then slowly creeps up to around 800 MB, it takes around 30 seconds to do so. There are no page requests being handled at this time. When I restart the website from IIS the memory size of the process does not alter.

I have tried running a debug copy of the application from VS 2010, there are no problems with memory usage.

Some ideas I have/questions are:

Is this problem related to the websites code? - Given that the memory rockets before any page requests have been sent/handled, I would assume this is NOT a code problem?

The application built in MVC has no handling of caching written into it.

The website uses real-time displaying of data, it uses ajax requests periodically, and is generally left 'open' for long periods of time.

Why does the memory usage rocket up after the application is recycled and no user requests are being sent? Is this because it is loading old cache information into it's memory from disk?

The application does NOT crash, I'm just concerned about the memory usage, it is not that big of a website...

Any ideas/help with getting to the bottom of this problem would be appreciated.

Answer 1

The best thing to do if you can afford to use a debugger is install the Windows Debugging Tools and use something like WinDbg and SOS.dll to figure out exactly what is it in memory.

once you've installed the tools then you can:

1. Launch Windbg.exe running elevated (as Administrator)
2. Use "File->Attach To Process" and choose w3wp.exe for the app you are trying to figure out. If you have many you can use Task Manager and add the command-line column to see the PID or use IIS Manager->Worker Processes to figure it out, and then choose that process in WinDBG.
3. run:
4. .loadby sos clr
5. !dumpheap -stat

At that point you should be able to see all types sorted by the most memory consumption so you can start with the ones at the bottom. (I would recommend exclude Strings, and Object since those are usually a side-effect and not the cause). Use "!dumpheap -type type-here" to find the instances and use !gcroot for those to figure out why they are in memory, maybe due to a static field, or an event handler leaked, WCF channels not disposed, or things like that are common sources.