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Asked: 2026-05-21T18:06:37+00:00

I have a fairly busy site which does around 10m views a month. One

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I have a fairly busy site which does around 10m views a month.

One of my app pools seemed to jam up for a few hours and I’m looking for some ideas on how to troubleshoot it..? I suspect that it somehow ran out of threads but I’m not sure how to determine this retroactively..? Here’s what I know:

  • The site never went ‘down’, but around 90% of requests started timing out.
  • I can see a high number of “HttpException – Request timed out.” in the log during the outage
  • I can’t find any SQL errors or code errors that would have caused the timeouts.
  • The timeouts seem to have been site wide on all pages.
  • There was one page with a bug on it which would have caused errors on that specific page.
  • The site had to be restarted.

The site is ASP.NET C# 3.5 WebForms..

Possibilities:

  1. Thread depletion: My thought is that the page causing the error may have somehow started jamming up the available threads?
  2. Global code error: Another possibility is that one of my static classes has an undiscovered bug in it somewhere. This is unlikely as the this has never happened before, and I can’t find any log errors for these classes, but it is a possibility.

UPDATE

I’ve managed to trace the issue now while it’s occurring. The pages are being loaded normally but for some reason WebResource.axd and ScriptResource.axd are both taking a minute to load. In the performance counters I can see ASP.NET Requests Queued spikes at this point.

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1 Answer

  1. Editorial Team

    The first thing I’d try is Sam Saffron’s CPU analyzer tool, which should give an indication if there is something common that is happening too much / too long. In part because it doesn’t involve any changes; just run it at the server.

    After that, there are various other debugging tools available; we’ve found that some very ghetto approaches can be insanely effective at seeing where time is spent (of course, it’ll only work on the 10% of successful results).

    You can of course just open the server profiling tools and drag in various .NET / IIS counters, which may help you spot some things.

    Between these three options, you should be covered for:

    • code dropping into a black hole and never coming out (typically threading related)
    • code running, but too slowly (typically data access related)
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