ASP.NET Performance Issue

I am working on an ASP.NET 3.5, C#, ASP.NET AJAX, JQUERY web application which currently is having some performance issues. I have a screen with the forms view control and when I edit the form and save it for the first time the POST takes 4.89 seconds and when I perform the same operation again for the second time the POST only takes 1.09 seconds. What could be the reason for this strange behavior?

Note: I am using firebug and I am disregarding the page resources (like js, images) load time.

EDIT: I am using the Web Deployment Project to precompile the applicat开发者_StackOverflow中文版ion.

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Are you on your local machine or on a production machine?

If this is the first time you build, remember .NET apps are usually quite slow when loading the first page. After that it usually picks up.

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Check that you have <compilation debug="false" /> within the <system.web> element of your Web.config files. It's a common issue that Scott Hanselman even mentioned on a recent post of the most common ASP.NET issues faced by MS support folks:

http://www.hanselman.com/blog/MostCommonASPNETSupportIssuesReportingFromDeepInsideMicrosoftDeveloperSupport.aspx

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If you precompile your ASP.NET application it will improve the performance of the first request. You can do this with the Publish tool in Visual Studio.