Maintaining Strong Cache Consistency in the World-Wide Web
Chengjie Liu and Pei Cao,
Computer Sciences Department,
University of Wisconsin-Madison,
Madison, WI 53706
cao@cs.wisc.edu
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Abstract
As the Web continues to explode in size, caching becomes increasingly important.
With caching comes the problem of cache consistency. Conventional wisdom
holds that strong cache consistency is too expensive for the Web, and
weak consistency methods such as Time-To-Live (TTL) are most appropriate.
This study compares three consistency approaches: {\em adaptive TTL},
{\em polling-every-time} and {\em invalidation}, using prototype
implementation and trace replay in a simulated environment.
Our results show that {\em invalidation} generates less or a comparable amount
of network traffic and server workload than {\em adaptive TTL} and has a
slightly lower average client response time, while {\em polling-every-time}
generates more network traffic and longer client response times.
We show that, contrary to popular belief, strong cache consistency can be
maintained for the Web with little or no extra cost than the current
weak consistency approaches, and it should be maintained using an
invalidation-based protocol.