document: Characterization of a large web site population with implications for content delivery This paper presents a systematic study of the properties of a large number of Web sites hosted by a major ISP . To our knowledge , ours is the first comprehensive study of a large server farm that contains thousands of commercial Web sites . We also perform a simulation analysis to estimate potential performance benefits of content delivery networks ( CDNs ) for these Web sites . We make several interesting observations about the current usage of Web technologies and Web site performance characteristics . First , compared with previous client workload studies , the Web server farm workload contains a much higher degree of uncacheable responses and responses that require mandatory cache validations . A significant reason for this is that cookie use is prevalent among our population , especially among more popular sites . However , we found an indication of wide-spread indiscriminate usage of cookies , which unnecessarily impedes the use of many content delivery optimizations . We also found that most Web sites do not utilize the cache-control features ofthe HTTP 1.1 protocol , resulting in suboptimal performance . Moreover , the implicit expiration time in client caches for responses is constrained by the maximum values allowed in the Squid proxy . Finally , our simulation results indicate that most Web sites benefit from the use of a CDN . The amount of the benefit depends on site popularity , and , somewhat surprisingly , a CDN may increase the peak to average request ratio at the origin server because the CDN can decrease the average request rate more than the peak request rate .
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