Maintaining Cache Consistency in Content Distribution Networks

While several mechanisms for maintaining consistency in single proxy caches exist today, not as much research has addressed ways in which such techniques may be extended to a cluster of proxy caches. If such techniques are not developed and deployed carefully, the overheads involved in maintaining cache consistency in large-scale systems such as Content Distribution Networks (CDNs) increases by several orders of magnitude with increase in the number of proxies. The goal of developing such algorithms is therefore to come up with ways by which consistency guarantees can be provided while keeping network and server resource usage low. In this paper, we present efficient ways to maintain cache consistency in CDNs using leases. We address the following issues: (i) Selection of a leader proxy, via which updates and/or invalidates may be propagated to other proxies (ii) The effects of co-operation between proxy caches (iii) Eager vs. Lazy renewal of leases (iv) Policies for intelligent dissemination of updates and/or invalidates. (v) Means of adapting to changing server and network loads and yet providing consistency guarantees. (vi) Multi-level hierarchical proxy organization and (vii) The scalability achieved with increasing number of independent proxy clusters.