Intermittent delays in System.Web.HttpApplication.BeginRequest(), not SessionState related

Question

We have two web apps (Azure web roles) that both suffer from occasional long delays (40 to 60 seconds) during System.Web.HttpApplication.BeginRequest. We know this because we are using NewRelic to monitor our web apps. The usual culprit is thread agility issues due to ASP.NET's Session State locking mechanism, however we don't use ASP.NET Session State, and on one of the sites we don't use sessions at all.

One app is much more complex than the other and suffers more delays, but I'll use the simple app in this question to hopefully narrow down the root cause.

The simple web app is a series of ServiceStack based web services. It does not use sessions. It only acts as intermediary to a WCF based service layer. It's mainly channeling the requests to WCF services and then mapping the response to views to transfer back to the agent. The servers don't even break a sweat at the loads they are running (max 2.5% CPU).

So, what is the likely cause please?

1. My best guess is that it is a thread agility issue as it seems to be waiting for something, which would suggest a lock somewhere. But what is it waiting for if not Session State? NewRelic or ServiceStack are causing the lock?
2. NewRelic's reporting is wrong, and there is no problem. Well, NewRelic correctly reported problems when we used to use ASP.NET Session State and were getting a lot more of these delays.

Answer 1

New Relic doesn't have instrumentation specific to ServiceStack and WCF is very basic without custom instrumentation. Without more information, it's very difficult to offer any advice. Thread agility is also a primary culprit and I'd recommend investigating that route first.

It is possible New Relic is attributing the time to a method it shouldn't. I would probably start by opening a ticket with New Relic Support and include all your info (agent logs, IIS/ASP.NET configuration, custom handlers? and permalinks to your New Relic graphs).