"Peer-to-peer" systems like Napster and Gnutella have recently become popular for sharing information. In this paper, we study the relevant issues and tradeoffs in designing a scalable P2P system. We focus on a subset of P2P systems, known as "hybrid" P2P, where some functionality is still centralized. (In Napster, for example, indexing is centralized, and file exchange is distributed.) We model a file-sharing application, developing a probabilistic model to describe query behavior and expected query result sizes. We also develop an analytic model to describe system performance. Using experimental data collected from a running, publicly available hybrid P2P system, we validate both models. We then present several hybrid P2P system architectures and evaluate them using our model. We discuss the tradeoffs between the architectures and highlight the effects of key parameter values on system performance.
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