HP Labs Technical Reports
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Characterizing Temporal Locality and its Impact on Web Server Performance
Cherkasova, Ludmila; Ciardo, Gianfranco
Keyword(s): workload case studies; web server logs; temporal locality; the scaled stack distance; synthetic web trace generators; performance analysis
Abstract: The presence of temporal locality in web request traces has long been recognized, and has been incorporated in synthetic web trace generators. However, the close proximity of requests for the same file in a trace can be attributed to two orthogonal reasons: long-term popularity and short-term correlation. The former reflects the fact that requests for a popular document simply appear "very frequently" thus they are likely to be "close" in an absolute sense. The latter reflects instead the fact that requests for a given document might concentrate around particular points in the trace due to a variety of reasons, such as deadlines or swings in user interests, hence it focuses on "relative" closeness. In this work, we introduce a new measure of temporal locality, the scaled stack distance, which is insensitive to popularity and captures instead the impact of short-term correlation. We then use the scaled stack distance observed in the original trace to parametrize a synthetic trace generator. Finally, we validate the appropriateness of using this quantity by comparing the file and byte miss ratios corresponding to either the original or the synthetic traces.
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