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Adaptive Leases: A Strong Consistency Mechanism for the World Wide Web
September/October 2003 (vol. 15 no. 5)
pp. 1266-1276

Abstract—In this paper, 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 1,030 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.

[1] R. Tewari, M. Dahlin, H.M. Vin, and J. Kay, Beyond Hierarchies: Design Considerations for Distributed Caching on the Internet Proc. 19th Int'l Conf. Distributed Computing Systems (ICDCS), June 1999.
[2] J. Gwertzman and M. Seltzer, World-Wide Web Cache Consistency Proc. 1996 USENIX Technical Conf., Jan. 1996.
[3] Squid Internet Object Cache Users Guide, available online athttp:/, 1997.
[4] P. Barford, A. Bestavros, A. Bradley, and M.E. Crovella, “Changes in Web Client Access Patterns: Characteristics and Caching Implications,” World Wide Web J. vol. 2, no. 1, pp. 15-28, Jan. 1999.
[5] V. Cate, Alex: A Global File System Proc. 1992 USENIX File System Workshop, pp. 1-12, May 1992.
[6] J. Yin et al., "Volume Leases for Consistency in Large-Scale Systems," IEEE Trans. Knowledge and Data Eng., vol. 11, no. 4, July/Aug. 1999.
[7] C. Gray and D. Cheriton, "Leases: An Efficient Fault-Tolerant Mechanism for Distributed File Cache Consistency," Proc. 12th Int'l Symp. Operating System Principles, 1989.
[8] P. Cao and C. Liu, Maintaining Strong Cache Consistency in the World-Wide Web Proc. 17th Int'l Conf. Distributed Computing Systems, May 1997.
[9] J. Yin, L. Alvisi, M. Dahlin, and C. Lin, Hierarchical Cache Consistency in a WAN Proc. Usenix Symp. Internet Technologies (USEITS '99), Oct. 1999.
[10] H. Yu, L. Breslau, and S. Shenker, A Scalable Web Cache Consistency Architecture Proc. ACM SIGCOMM '99, Sept. 1999.
[11] E. Cohen, B. Krishnamurthy, and J. Rexford, Improving End-to-End Performance of the Web Using Server Volumes and Proxy Filters Proc. ACM Conf. Applications, Technologies, Architectures and Protocols for Computer Comm. (ACM SIGCOMM '98), pp. 241-253, Aug. 1998.
[12] J. Mogul et al., "Potential Benefits of Delta-Encoding and Data Compression for HTTP," Proc. ACM SIGCOMM, ACM Press, New York, 1997, pp. 181-194. An extended and corrected version appears as Research Report 97/4a, Digital Equipment Corp. Western Research Laboratory, Dec. 1997.
[13] B. Krishnamurthy and C. Wills, Proxy Cache Coherency and Replacement Towards a More Complete Picture Proc. 19th Int'l Conf. Distributed Computing Systems (ICDCS), June 1999.
[14] L. Breslau, P. Cao, L. Fan, G. Phillips, and S. Shenker, Web Caching and Zipf-Like Distributions: Evidence and Implications Proc. Infocom '99, Mar. 1999.
[15] V. Duvvuri, Adaptive Leases: A Strong Consistency Mechanism for the World Wide Web MS thesis, Univ. of Mass., June 1999.
[16] P.M. Chen and D.A. Patterson, "Maximizing Performance in a Striped Disk Array," Proc. 17th Int'l Symp. Computer Architecture,Seattle, pp. 322-331, May 1990.
[17] Seagate Technology, Inc., ST-11200N SCSI-2 Fast (Barracuda 4) Specification, Aug. 1994.
[18] A. Ninan, P. Kulkarni, P. Shenoy, K. Ramamritham, and R. Tewari, Scalable Consistency Maintenance in Content Distribution Networks Technical Report TR00-29, Dept. of Computer Science, Univ. of Mass. at Amherst, July 2001.

Index Terms:
Web caching, Web proxy servers, cache consistency, strong consistency, leases.
Venkata Duvvuri, Prashant Shenoy, Renu Tewari, "Adaptive Leases: A Strong Consistency Mechanism for the World Wide Web," IEEE Transactions on Knowledge and Data Engineering, vol. 15, no. 5, pp. 1266-1276, Sept.-Oct. 2003, doi:10.1109/TKDE.2003.1232277
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