USENIX Symposium on Internet Technologies and Systems, 1997
Study of Piggyback Cache Validation for Proxy Caches in the World Wide Web
AT&T Labs - Research
Craig E. Wills
Worcester Polytechnic Institute
This paper presents work on piggyback cache validation (PCV), which
addresses the problem of maintaining cache coherency for proxy
caches. The novel aspect of our approach is to capitalize on requests
sent from the proxy cache to the server to improve coherency. In the
simplest case, whenever a proxy cache has a reason to communicate with
a server it piggybacks a list of cached, but potentially stale,
resources from that server for validation.
Trace-driven simulation of this mechanism on two large, independent data
sets shows that PCV both provides stronger cache coherency and reduces the
request traffic in comparison to the time-to-live (TTL) based techniques
currently used. Specifically, in comparison to the best TTL-based policy,
the best PCV-based policy reduces the number of request messages from a
proxy cache to a server by 16-17% and the average cost (considering
response latency, request messages and bandwidth) by 6-8%. Moreover, the
best PCV policy reduces the staleness ratio by 57-65% in comparison to the
best TTL-based policy. Additionally, the PCV policies can easily be
implemented within the HTTP 1.1 protocol.
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