Why we are using warm-up scripts

SharePoint is built upon the Microsoft .NET Framework and ASP.NET, specially the 2.0 releases of those technologies. ASP.NET is architected so that its pages are not compiled until the first time a server request .As you know when an IIS worker process has coming up for the first time , It makes lots of jobs in the background. The big portion of this time used by compiling assemblies, and reading configurations  . For a standard ASP.Net application it takes very small time but for a SharePoint Application we have tons of assemblies and configurations and more than one WCF services which is need to be activated . So it will usually takes more time over 1 minutes. The warm up duration also depends on your configuration , hardware and assembly counts and changes for every system.

The issue happens when application pool recycle, iisreset or a worker process crashes.  And for SharePoint sites every application pool has a configuration that force the recycle itself . You can check from IIS -> Application Pools -> (For example Select “SharePoint Central Administration v4”) and right click   Select Recycling option And you can see the recycle time.

We have also an Idle Time Out property defined in Application Pool settings that make free worker processes resources which are in idle state for defined time period . Configure Idle Time-out Settings for an Application Pool (IIS 7) http://technet.microsoft.com/en-us/library/cc771956(v=WS.10).aspx

However even it is disabled by setting “Idle Time Out” value to 0 still IIS requires and also suggested way that recycle application pools daily manner. The default IIS behavior of naturally cycling an app pool somewhere between 1am and 3am or off hours if there is such a thing is healthy to clean out the memory space in IIS. Also same consideration is valid for SharePoint Timer service , there is a Timer job in SharePoint for responsible to restart timer service in daily manner. It is a good and suggested thing http://blogs.msdn.com/b/besidethepoint/archive/2012/01/10/the-timer-recycle-job-job-timer-recycle.aspx

But sometime in the midnight a recycle occurs and assume that no one send a request a server until morning and when a user open his browser and try to connect SharePoint site He/She should wait more, because the worker process is only getting up until the first time a server get the request. Warm up scripts send a requests to your server for a scheduled time  that forces IIS to worker process up and running .when a user’s request a page through a browser, preventing your users from seeing a delay when making that first request. That’s pretty much all they do, and the only purpose most of them serve is to “warm up” your server by having precompile your site’s ASP.NET pages ahead of an actual user request. You can use warm up scripts .

For the warm up scripts which is described in fallowing article http://blogs.technet.com/b/rgullick/archive/2011/12/02/minimalist-sharepoint-warmup-script.aspx have very common usage on this kind of issues.