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<p><b>Abstract</b>—In this paper, we argue that cache consistency mechanisms designed for stand-alone proxies do not scale to the large number of proxies in a content distribution network and are not flexible enough to allow consistency guarantees to be tailored to object needs. To meet the twin challenges of scalability and flexibility, we introduce the notion of <it>cooperative consistency</it> along with a mechanism, called <it>cooperative leases</it>, to achieve it. By supporting <tmath>\Delta{\hbox{-}}{\rm{consistency}}</tmath> semantics and by using a single lease for multiple proxies, cooperative leases allow the notion of leases to be applied in a flexible, scalable manner to CDNs. Further, the approach employs application-level multicast to propagate server notifications to proxies in a scalable manner. We implement our approach in the Apache Web server and the Squid proxy cache and demonstrate its efficacy using a detailed experimental evaluation. Our results show a factor of <tmath>2.5</tmath> reduction in server message overhead and a <tmath>20</tmath> percent reduction in server state space overhead when compared to original leases albeit at an increased interproxy communication overhead.</p>
Dynamic data, data consistency, data dissemination, World Wide Web, scalability, leases, push, pull, content distribution networks.

P. Kulkarni, P. Shenoy, A. G. Ninan, R. Tewari and K. Ramamritham, "Scalable Consistency Maintenance in Content Distribution Networks Using Cooperative Leases," in IEEE Transactions on Knowledge & Data Engineering, vol. 15, no. , pp. 813-828, 2003.
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