Microsoft_Press_ebook_Introducing_Windows_Server_2012_R2_PDF.pdf

Idle worker process page out a second scalability

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The Configuration Editor configures Dynamic Site Activation. Idle Worker Process Page-out A second scalability issue that can be experienced on IIS servers hosting large numbers of sites has to do with cold requests. A cold request is a request that comes for a worker process that has not yet been started. The cold request has to wait for IIS to initialize, for the appropriate framework (for example, .NET or PHP) to initialize, for the associated site to initialize, and so on. As a result, the response time to cold requests with previous versions of IIS sometimes left something to be desired. This issue was partly addressed with IIS 8 in Windows Server 2012 where static sites responded much more quickly (typically a few hundred milliseconds) to cold requests than for IIS 7 in Windows Server 2008 R2. However, there was only a small performance improvement in IIS 8 for dynamic sites with managed code, with such sites typically taking several seconds to start in response to cold requests, largely because of the time needed to load the application framework needed by the site. From the perspective of the hoster’s customers, however, taking several seconds to launch their LOB web application can be viewed negatively as unacceptable and poor performance. To improve the start time for dynamic sites in response to cold requests, a module called Application Initialization, was included in IIS 8 in Windows Server 2012 that allowed the administrator to preload the application framework needed for a dynamic site so that the site could respond to a cold request in a few hundred milliseconds instead of several seconds. However, this module is not useful for hosters because such preloaded application
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Idle Worker Process Page-out CHAPTER 8 157 frameworks consume additional memory for each site configured to use them. Since the IIS servers of a hoster are typically hosting thousands of sites and are usually memory-bound (assume at least 100 MB needed per dynamic site), such preloading application frameworks for all sites hosted on a server just wasn’t feasible. IIS can partly address this problem by killing idle worker processes after a default of 20 minutes of inactivity, and WAS can halve this time interval if it determines that memory pressure has reached 80 percent on the server. IIS 8.5 in Windows Server 2012 R2 now takes a different perspective on how to address the problem of cold request delays for dynamic sites. A new feature called Idle Worker Process Page-out, saves memory by allowing an idle worker process to be paged to disk so that the worker process is removed from memory. The page-out feature can be made to perform even better by utilizing a solid state disk (SSD) for the paging file of an IIS server. The result is that memory pressure can now be greatly reduced for servers hosting thousands of dynamic sites and the response time to cold requests for these sites can be significantly improved.
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