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USENIX 2004 Annual Technical Conference, General Track — Abstract

Awarded Best Paper!

Pp. 127–140 of the Proceedings

Handling Churn in a DHT

Sean Rhea and Dennis Geels, University of California, Berkeley; Timothy Roscoe, Intel Research, Berkeley; John Kubiatowicz, University of California, Berkeley


This paper addresses the problem of churn—the continuous process of node arrival and departure—in distributed hash tables (DHTs). We argue that DHTs should perform lookups quickly and consistently under churn rates at least as high as those observed in deployed P2P systems such as Kazaa. We then show through experiments on an emulated network that current DHT implementations cannot handle such churn rates. Next, we identify and explore three factors affecting DHT performance under churn: reactive versus periodic failure recovery, message timeout calculation, and proximity neighbor selection. We work in the context of a mature DHT implementation called Bamboo, using the ModelNet network emulator, which models in-network queuing, cross-traffic, and packet loss. These factors are typically missing in earlier simulation-based DHT studies, and we show that careful attention to them in Bamboo's design allows it to function effectively at churn rates at or higher than that observed in P2P file-sharing applications, while using lower maintenance bandwidth than other DHT implementations.
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