ASP.NET WebMethod Performance Issue in loading Context

Question

I have a WebMethod which is used to return some HTML into a page after the initial load. The method is called through jQuery's ajax methods.

Everything works, however, there is a rather serious performance issue in loading the request state from these calls. With significant traffic CPU usage maxes out and actually kills the responsiveness of the entire site.

Using one profiler, System.Web.Handlers.ScriptModule.OnPostAcquireRequestState() is called out as the culprit with almost 100% of the call's duration.

Another profiler calls out System.Web.HttpApplication.System.Web.IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, object extraData).

So I can reproduce the behavior locally with a load test, but with the culprit in the library I'm at a loss as to how to address it. Are there any 'gotchas' that can cause the context to be expensive to recover? Can I simply remove the context from the WebMethod?

ccook · Accepted Answer · 2013-04-19 12:40:18Z

2

It turned out the problem was having the WebMethod within the Page class. This forced the WebMethod to load with Session State, which has a reader/writer lock on the Session object. This forced the requests to execute synchronously, queuing up requests waiting for the lock to open.

I could not force the WebMethod within the page to not load the Session, or even load it as read only. Moving the WebMethod into its own WebService allowed this - and solved the problem.

This resolved the CPU 'lockup' on entering the WebMethod, and allowed the methods to execute concurrently greatly helping the page's load time.

answered Apr 19, 2013 at 12:40

ccook

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4 Comments

DarrenMB Over a year ago

You will notice that "WebMethod" Attribute also has an "EnableSession=False" option you can put directly in the WebMethod to prevent this locking. VB <WebMethod(BufferResponse:=False, EnableSession:=False)>

ccook Over a year ago

If I recall correctly, it was a few years ago, the issue was that disabling the session on the web method does not work when it is within a page class.

GP24 Over a year ago

Has anyone got links to docs or articles on this? WebMethod in a page forces session? Just looking at it and not seeing much...

ccook Over a year ago

@GP24, had to view decompilled code to figure it out.

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