document: Cooperative leases : scalable consistency maintenance in content distribution networks 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 cooperative consistency along with a mechanism , called cooperative leases , to achieve it . By supporting & Dgr ; - consistency semantics and by using a single lease for multiple proxies , cooperative leases allows 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 2.5 reduction in server message overhead and a 20 % reduction in server state space overhead when compared to original leases albeit at an increased inter-proxy communication overhead .
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