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This paper studies mechanisms and policies for supporting HTTP/1.1
persistent connections in cluster-based Web servers that employ
content-based request distribution. We present two mechanisms for the
efficient, content-based distribution of HTTP/1.1 requests among the
back-end nodes of a cluster server. A trace-driven simulation shows
that these mechanisms, combined with an extension of the
locality-aware request distribution (LARD) policy, are effective in
yielding scalable performance for HTTP/1.1 requests. We implemented
the simpler of these two mechanisms, back-end forwarding.
Measurements of this mechanism in connection with extended LARD on
a prototype cluster, driven with traces from actual Web servers,
confirm the simulation results. The throughput of the prototype is
up to four times better than that achieved by conventional weighted
round-robin request distribution. In addition, throughput with
persistent connections is up to 26% better than without.
Peter Druschel
1999-04-27