Chapter2_Caching - The World Wide Web Caching The WWW can...

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1 Caching The World Wide Web ± The WWW can be considered as a large distributed information system. ± Exponential growth in size. ± On may 1999 included 600 millions of static web pages. ± Increases 15% per month. ± Very popular. 0 100 200 300 400 500 600 Jun-97 Nov-97 Mar-98 May-99 SIZE OF DISTINCT STATIC WEB PAGES The World Wide Web ± Usage is relatively inexpensive ± Accessing information is very fast ± Documents appeal to a wide range of interests ± But…. . ± Network congestion ± Server overloading ± Problem ± Internet backbone capacity increases 60% per year. ± Bandwidth is not growing fast enough. ± Without solution WWW will become too congested and its entire appeal would be lost. Solution ± Caching: Placing popular objects at locations close to the clients. Advantages of web caching ± Reduces bandwidth consumption Decreases network traffic Lessens network congestion ± Access latency: ± frequently used docs are cached nearby ± less traffic Æ shorter delay for docs not cached Advantages of web caching (cont.) ± Reduces workload of remote server ± Data can be accessed when remote server is down (enhanced robustness). ± Allows analysis of organization usage patterns ² cooperation between caches increases efficiency.
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2 Disadvantages of web caching ± Data not updated automatically ± Cache miss can cause increase in latency (extra proxy processing). ± Bottleneck effect – limit # of clients per proxy. ± A single proxy is a single point of failure ± Information providers can not monitor # of visits per site. Elements of A WWW caching system Documents can be cached at the clients , the proxies and the servers . Web server Web server Proxy server cooperation clients Elements of a WWW caching system request client Does proxy have requested page yes no Does cooperative proxies have web page Find web page on server Desirable properties of WWW caching system ± fast access ± robustness ± transparency ± scalability ± efficiency ± adaptivity ± stability ± load balance ± ability to deal with heterogeneity ± simplicity What Problems do we face in designing caching systems for the WWW ??? Problem 1: Caching System Architecture How cache proxies are organized – hierarchically, distributed or hybrid?
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3 national regional institutional bottom web page not found web page not found web page not found ± Caches are placed at multiple levels of the network.
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This note was uploaded on 10/27/2009 for the course CSE 830 taught by Professor Ofria during the Fall '08 term at Michigan State University.

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Chapter2_Caching - The World Wide Web Caching The WWW can...

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