Large-scale content delivery systems such as the Web often deploy multiple caches at different locations to reduce access latency and network traffic. These caches are usually organized in a cascaded fashion where requests not hitting a lower level cache are forwarded to a higher level cache. The performance of cascaded caching depends on how the cache contents are managed, including object placement and replacement schemes. We present a general analytical framework for coordinated management of cascaded caches. The object placement problem is formulated as an optimization problem and the optimal locations for caching objects are computed by a dynamic programming algorithm. Based on the framework, we propose a novel caching scheme that incorporates both object placement and replacement strategies. The proposed scheme makes caching decisions for the set of caches lying on the delivery path of a request in a coordinated fashion. Simulation experiments based on real traces from Web caches have been conducted under two different cascaded caching architectures: enroute caching and hierarchical caching. The results show that for both architectures, the proposed scheme significantly outperforms existing schemes that consider object placement or replacement at individual caches only.
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