On the sensitivity of cooperative caching performance to workload and network characteristics

ABSTRACT

A rich body of literature exists on several aspects of cooperative caching [1, 2, 3, 4, 5], including object placement and replacement algorithms [1], mechanisms for reducing the overhead of cooperation [2, 3], and the performance impact of cooperation [3, 4, 5]. However, while several studies have focused on quantifying the performance benefit of cooperative caching, their conclusions on the effectiveness of such cooperation vary significantly. The source of this apparent disagreement lies mainly in their different assumptions about workload and network characteristics, and about the degree of cooperation among caches.To more comprehensively evaluate the practical benefit of cooperative caching, we explore the sensitivity of the benefit of cooperation to workload characteristics such as object popularity distribution, temporal locality, one time referencing behavior, and to network characteristics such as latencies between clients, proxies, and servers. Furthermore, we identify a critical workload characteristic, which we call average access density, and show that it has a crucial impact on the effectiveness of cooperative caching.In this extended abstract, we report on a few important results selected from our extensive study reported in [6]. In particular, assuming an LFU-based cache management policy, we arrive at the following conclusions. First, cooperative caching is only effective when the average access density (defined as the ratio of the number of requests to the number of distinct objects in a time window) is relatively high. Second, the effectiveness of cooperative caching decreases as the skew in object popularity increases. Higher skew means that only a small number of objects are most frequently accessed reducing the benefit of larger caches, and therefore of cooperation.

REFERENCES

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