Coordinated Placement and Replacement for Large-Scale Distributed Caches

In a large-scale information system such as a digital library or the web, a set of distributed caches can improve their effectiveness by coordinating their data placement decisions. Using simulation, we examine three practical cooperative placement algorithms including one that is provably close to optimal, and we compare these algorithms to the optimal placement algorithm and several cooperative and non-cooperative replacement algorithms. We draw five conclusions from these experiments: (1) cooperative placement can significantly improve performance compared to local replacement algorithms particularly when the size of individual caches is limited compared to the universe of objects; (2) although the amortizing placement algorithm is only guaranteed to be within 14 times the optimal, in practice it seems to provide an excellent approximation of the optimal; (3) in a cooperative caching scenario, the recent greedy-dual local replacement algorithm performs much better than th..