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.

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.

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

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.