We analyze replication of resources by server nodes that act selfishly, using a game-theoretic approach. We refer to this as the selfish caching problem. In our model, nodes incur either cost for replicating resources or cost for access to a remote replica. We show the existence of pure strategy Nash equilibria and investigate the price of anarchy, which is the relative cost of the lack of coordination. The price of anarchy can be high due to undersupply problems, but with certain network topologies it has better bounds. With a payment scheme the game can always implement the social optimum in the best case by giving servers incentive to replicate.

The rapid growth of time-critical information services and business-oriented applications is making quality of service (QoS) support increasingly important in content distribution. This paper investigates the problem of placing object replicas (e.g., web pages and images) to meet the QoS requirements of clients with the objective of minimizing the replication cost. We consider two classes of service models: replica-aware service and replica-blind service. In the replica-aware model, the servers are aware of the locations of replicas and can therefore direct requests to the nearest replica. We show that the QoS-aware placement problem for replica-aware services is NP-complete. Several heuristic algorithms for efficient computation of suboptimal solutions are proposed and experimentally evaluated. In the replica-blind model, the servers are not aware of the locations of replicas or even their existence. As a result, each replica only serves the requests flowing through it under some given routing strategy. We show that there exist polynomial optimal solutions to the QoS-aware placement problem for replicablind services. Efficient algorithms are proposed to compute the optimal locations of replicas under different cost models.

Abstract—The rapid growth of new information services and business-oriented applications entails the consideration of quality of service (QoS) in content distribution. This paper investigates the QoS-aware replica placement problems for responsiveness QoS requirements. We consider two classes of service models: replica-aware services and replica-blind services. In replica-aware services, the servers are aware of the locations of replicas and can therefore optimize request routing to improve responsiveness. We show that the QoS-aware placement problem for replica-aware services is NP-complete. Several heuristic algorithms for fast computation of good solutions are proposed and experimentally evaluated. In replica-blind services, the servers are not aware of the locations of replicas or even their existence. As a result, each replica only serves the requests flowing through it under some given routing strategy. We show that there exist polynomial optimal solutions to the QoS-aware placement problem for replica-blind services. Efficient algorithms are proposed to compute the optimal locations of replicas under different cost models. Index Terms—Content distribution, replication, placement, quality of service, dynamic programming, NP-complete. 1

Proxy caching is an effective technique to reduce the network resources consumed by web services as well as the access latencies perceived by web users. This article discusses the issues and challenges of deploying web caching proxies over the Internet. We focus on the cache management for conventional web objects such as HTML pages and images and present the state-of-the-art solutions to various cache management problems including prefetching, consistency maintenance, and cooperative caching. We also highlight several possible research directions with the emerging applications and services.

In a multi-level cache such as those used for web caching, a hit at level l leads to the caching of the requested object in all intermediate caches on the reverse path (levels l − 1,...,1). This paper shows that a simple modification to this de facto behavior, in which only the l − 1 level cache gets to store a copy, can lead to significant performance gains. The modified caching behavior is called Leave Copy Down (LCD); it has the merit of being able to avoid the amplification of replacement errors and also the un-necessary repetitious caching of the same objects at multiple levels. Simulation results against other cache interconnections show that when LCD is applied under typical web workloads, it reduces the average hit distance. We construct an approximate analytic model for the case of LCD interconnection of LRU caches and use it to gain a better insight as to why the LCD interconnection yields an improved performance.

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Large scale hierarchical caches for web content have been deployed widely in an attempt to reduce delivery delays and bandwidth consumption and also to improve the scalability of content dissemination through the world wide web. Irrespectively of the specific replacement algorithm employed in each cache, a de facto characteristic of contemporary hierarchical caches is that a hit for a document at an $l$-level cache leads to the caching of the document in all intermediate caches (levels $l-1,\ldots,1$) on the path towards the leaf cache that received the initial request. This paper presents various algorithms that revise this standard behavior and attempt to be more selective in choosing the caches that get to store a local copy of the requested document. As these algorithms operate independently of the actual replacement algorithm running in each individual cache, they are referred to as \emph{meta algorithms}. Three new meta algorithms are proposed and compared against the de facto one and a recently proposed one by means of synthetic and trace-driven simulations. The best of the new meta algorithms appears to be leading to improved performance under most simulated scenarios, especially under a low availability of storage. The latter observation makes the presented meta algorithms particularly favorable for the handling of large data objects such as stored music files or short video clips. Additionally, a simple load balancing algorithm that is based on the concept of meta algorithms is proposed and evaluated. The algorithm is shown to be able to provide for an effective balancing of load thus possibly addressing the recently discovered ``filtering-effect'' in hierarchical web caches. -level cache leads to the caching of the document in all intermediate caches (levels########## ) on the path towards the leaf cache that received the initial request. This paper presents various algorithms that revise this standard behavior and attempt to be more selective in choosing the caches that get to store a local copy of the requested document. As these algorithms operate independently of the actual replacement algorithm running in each individual cache, they are referred to as meta algorithms. Three new meta algorithms are proposed and compared against the de facto one and a recently proposed one by H. Che, Y. Tung, and Z. Wang [1] by means of synthetic and trace-driven simulations. The best of the new meta algorithms appears to be able to lead to improved performance under most simulated scenarios, especially under a low availability of storage. The latter observation makes the presented meta algorithms particularly favorable for the handling of large data objects such as stored music files or short video clips. Additionally, a simple load balancing algorithm that is based on the concept of meta algorithms is proposed and evaluated. The algorithm is shown to be able to provide for an effective balancing of load thus possibly addressing the recently discovered "filtering-effect" in hierarchical web caches (C. Williamson [2]).

In recent years, the World Wide Web, or simply the Web

This paper studies the optimal placement of web files for en-route web caching. It is shown that existing placement policies are all solving restricted partial problems of the file placement problem, and therefore give only sub-optimal solutions. A dynamic programming algorithm of low complexity which computes the optimal solution is presented. It is shown both analytically and experimentally that the file-placement solution output by our algorithm outperforms existing enroute caching policies. The optimal placement of web files can be implemented with a reasonable level of cache coordination and management overhead for en-route caching; and importantly, it can be achieved with or without using data prefetching.

Abstract—For several years, web caching has been used to meet the ever increasing Web access loads. A fundamental capability of all such systems is that of inter-cache coordination, which can be divided into two main types: explicit and implicit coordination. While the former allows for greater control over resource allocation, the latter does not suffer from the additional communication overhead needed for coordination. In this paper, we consider a network in which each router has a local cache that caches files passing through it. By additionally storing minimal information regarding caching history, we develop a simple content caching, location, and routing systems that adopts an implicit, transparent, and best-effort approach towards caching. Though only best effort, the policy outperforms classic policies that allow explicit coordination between caches. I.