The routing tables of Distributed Hash Tables (DHTs) can vary from size O(1) to O(n). Currently, what is lacking is an analytic framework to suggest the optimal routing table size for a given workload. This paper (1) compares heterogeneous DHTs with O(1) to O(n) routing tables and identies the good design points for typical workloads; and (2) proposes practical protocols to realize the potential of those good design points. We validate our protocols through both analysis and extensive simulation.
Our comparison is novel in two aspects. First, we compare totally heterogeneous DHTs and use capacity as the uniform metric to evaluate them. Second, we emphasize that a good design should strike a balance between maintenance cost and lookup cost. Our analysis shows that, for typical workloads, large routing tables actually lead to both low total traffic and low lookup hops. These good design points translate into one-hop routing for systems of medium size and two-hop routing for large systems.
Existing one-hop or two-hop protocols are based on a hierarchy. We instead demonstrate that it is possible to achieve one-hop or two-hop routing without giving up being peer-to-peer. We propose 1h-Calot for one-hop routing and 2h-Calot for two-hop routing. They are purely peer-to-peer, efficient in traffic, and resilient in the face of frequent node arrivals and departures. Moreover, they are extremely simple for practical uses. Compared with traditional DHTs that use O(log n) routing tables, 1h-Calot and 2h-Calot save total traffic by up to 70% under typical workloads, while resolving lookups in one or two hops as opposed toO(log n) hops.
By: Chunqiang Tang; Melissa J. Buco; Rong N. Chang; Sandhya Dwarkadas; Laura Z. Luan; Edward So; Christopher Ward
Published in: RC23515 in 2005
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