Craig Wills, Worcester Polytechnic Institute, 100 Institute Road, Worcester, Massachusetts 01609, U.S.A. cew@cs.wpi.edu
Paul Thomas, Victoria University of Wellington, P.O. Box 600, Wellington, New Zealand. paul.thomas@vuw.ac.nz
Web Caching; Internet Costs; Prefetching
Caching proxies in the World Wide Web have traditionally been used to reduce overall latency and bandwidth by keeping copies of popular documents closer to the client than the server. This paper describes work to make such caches more sensitive to differential costs, in particular the distinction between relatively cheap ``off-peak'' and expensive ``on-peak'' network traffic. The idea is to develop algorithms that actively shape traffic patterns. Three methods were implemented and tested: prefetching, fetching a document ahead of an anticipated on-peak request; postfetching, fetching a document during off-peak time after an on-peak request; and not fetching, returning a potentially stale, cached copy from cache when retrieving a new copy may prove expensive.
The results show that postfetching is the most deterministic approach for reducing costs at the expense of some user inconvenience. Prefetching is not a desirable approach in the general case, but could be effectively used on a limited basis for objects with known change characteristics. The not fetching approach shows a small cost reduction with a comparable increase in stale cache objects served.
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