WCF (.NET 4.0) long delay in AuthenticateRequest state in IIS

We have a set of WCF (.NET 4.0) s开发者_运维问答ervices hosted in IIS7. We recently observed strange behaviour on production:

In IIS7 we opened the 'Current requests in the worker process' view for one of them (the most often called) and noticed that many request are listed in AuthenticateRequest state (ModuleName = ServiceModel-4.0) with time elapsed reaching up to a few seconds and then they disappear. We don't really use any authentication in this service.

AuthenticateRequest is a very early stage in the pipeline and we're wondering what could be holding them up there? We tried increasing the maxConcurrentCalls limit but that didn't seem to have any effect.

• Is this abnormal behaviour?
• I assume our application code has not been executed at this stage, yet, is this correct?
• If this is a contention of some sort what could be the problematic resource? We have mutliple WCF services running on that machine.

Thanks, Piotr

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We got an explanation on the MSDN WCF forum (http://social.msdn.microsoft.com/Forums/en-US/wcf/thread/c6045491-d266-431e-8c02-dbdece5dd1bd/#e573f8e0-2ca5-4514-a635-eadb2cb848a5).

It is the actual application code that is executing here.

Thanks, Piotr