The continued growth of the World-Wide Web and the emergence of new end-user technologies such as cable modems necessitate
the use of proxy caches to reduce latency, network traffic and Web server loads. In this paper we analyze the importance of
different Web proxy workload characteristics in making good cache replacement decisions. Trace-driven simulation is used to
evaluate the effectiveness of various replacement policies for Web proxy caches. The extended duration of the trace (117 million
requests collected over five months) allows long term side effects of replacement policies to be identified and quantified.
Our results indicate that size-based replacement policies maximize request hit rates while frequency-based policies maximize
byte hit rates. With either approach it is important that inactive objects be removed from the cache to prevent pollution.