Coordinated Data Prefetching by Utilizing Reference Information at Both
Proxy and Web Servers

Xin Chen and Xiaodong Zhang

Proceedings of the 2nd ACM Workshop on Performance and Architecture of
Web Servers, (PAWS-2001), Boston, Massachusetts, June 16-17, 2001.

Abstract

Existing prefetching techniques rely on server-based, proxy-based, or
client-based reference access information.  Although Web servers may
provide accurate access information, our studies show that significant
communication overhead can be involved by sending unnecessary reference
information to clients or/and proxy servers.  Our study also shows that
prediction accuracy of proxy-based prefetching can be significantly
limited without input of Web servers.  We propose a coordinated
proxy-server prefetching technique that adaptively utilizes the reference
information and coordinates prefetching activities at both proxy and web
servers. We have carefully considered the trade-off between the accuracy
of server information and the high cost of obtaining the information
in prefetching method designs.  In our design, the reference access
information stored in proxy servers will be the main source serving
data prefetching for groups of clients, each of whom shares the common
surfing interests.  The access information in the web server will be used
to serve data prefetching only for data objects that are not qualified
for proxy-based prefetching.

Conducting trace-driven simulations, we have quantified the limits
of both server-based and proxy-based prefetching, and evaluated
the proposed coordinated proxy-server prefetching technique to show
its effectiveness.  We show that both hit ratios and byte hit ratios
contributed from coordinated proxy-server prefetching are are up to 88%
higher than that from proxy-based prefetching, and they are comparable
to the ratios from server-based prefetching with a difference of 5%.

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