A full cache means all or at least most of the

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Unformatted text preview: om Steve Souders moved to Google as Head Performance Engineer and his work is now featured at: stevesouders.com Tenni Theurer moved to VISA as Sr. PM Director. Copyright 2009 - 2013 Horowitz 6 Browser Cache Experiment An “empty cache” means the browser bypasses the disk cache and has to request all the components to load the page. •  A “full cache” means all (or at least most) of the components are found in the disk cache and the corresponding HTTP requests are avoided •  Experiment: Try to determine what the percentage of people is who load a home page when there are no elements of the page in the user’s cache? •  SoluOon: add a new image (a pixel) to your page, e.g. <img src=“image/blank.gif” height=“1” width=“1”/> •  With the following response headers: Expires: thu, 15 Apr 2008 20:00:00 GMT (an earlier date than today) Last-Modified: Wed, 28 Sep 2009 23:49:57 GMT (today’s date) •  The Expires makes sure the page is not cached; the Last- Modified makes sure the server will have to check if blank.gif has changed •  Requests from a browser will produce one of these response status codes –  200 – the server is sending back the image implying the browser does not have the image in its cache –  304 – the browser has the image in its cache, and the server responds saying it has not been modified •  Compute the following numbers: •  –  –  Percentage of users who view with an empty cache ::= •  (# unique users with at least one 200 response)/(total # unique users) Percentage of page views that are done with an empty cache ::= •  (total # of 200 responses) / (# of 200 + # of 304 responses) Copyright 2009 - 2013 Horowitz 7 Surprising Results Lessons: The empty cache user is more prevalent than one might think users with empty cache page views with empty cache 100.0% 90.0% unique users with empty cache 40-60% ~20% 80.0%...
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