Adaptive leases: a strong consistency mechanism for the World Wide Web

We argue that weak cache consistency mechanisms supported by existing Web proxy caches must be augmented by strong consistency mechanisms to support the growing diversity in application requirements. Existing strong consistency mechanisms are not appealing for Web environments due to their large sta...

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Bibliographic Details
Published in:IEEE transactions on knowledge and data engineering 2003-09, Vol.15 (5), p.1266-1276
Main Authors: Duvvuri, V., Shenoy, P., Tewari, R.
Format: Article
Language:English
Subjects:
Analytical models
Consistency
Delay
Humans
Internet
Leases
Mathematical analysis
Messages
Network servers
Optimization
Protocols
Proxy client servers
State-space methods
Studies
Tradeoffs
Web server
Web sites
World Wide Web
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Summary:We argue that weak cache consistency mechanisms supported by existing Web proxy caches must be augmented by strong consistency mechanisms to support the growing diversity in application requirements. Existing strong consistency mechanisms are not appealing for Web environments due to their large state space or control message overhead. We focus on the lease approach that balances these trade-offs and present analytical models and policies for determining the optimal lease duration. We present extensions to the HTTP protocol to incorporate leases and then implement our techniques in the Squid proxy cache and the Apache Web server. Our experimental evaluation of the leases approach shows that: 1) our techniques impose modest overheads even for long leases (a lease duration of 1 hour requires state to be maintained for 1030 leases and imposes an per-object overhead of a control message every 33 minutes), 2) leases yields a 138-425 percent improvement over existing strong consistency mechanisms, and 3) the implementation overhead of leases is comparable to existing weak consistency mechanisms.
ISSN:1041-4347
1558-2191
DOI:10.1109/TKDE.2003.1232277