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Handling Churn in a DHT

Rhea, Sean
Geels, Dennis
Roscoe, Timothy
Kubiatowicz, John
Technical Report Identifier: CSD-03-1299
December 2003

Abstract: This paper addresses the problem of churn -- the continuous process of node arrival and departure -- in distributed hash tables (DHTs). We demonstrate through experiment that existing DHT implementations break down at churn levels observed in deployed peer-to-peer systems, contrary to simulation-based results. We present Bamboo, a DHT that handles high levels of churn, and discuss the manner in which it does so. We show that Bamboo is able to function effectively for median node session times as short as 1.4 minutes, while using less than 900 bytes/s/node of maintenance bandwidth in a 1000-node system. This churn rate is faster than that observed in real file-sharing systems such as Gnutella, Kazaa, Napster, and Overnet. Since Bamboo's bandwidth usage scales logarithmically in the number of nodes, we expect this cost to remain within the reach of dialup modems even for very large systems. Moreover, in simulated networks without churn, Bamboo achieves lookup performance comparable with Pastry, an existing DHT with a similar structure.