In peer-to-peer (P2P) systems, computers from around the globe share data and can participate in distributed computation. P2P became famous, and infamous, due to file-sharing systems like Napster. However, the scalability and robustness of these systems make them appealing to a wide range of applications. This article introduces P-Ring, a new peer-to-peer index structure. P-Ring is fully distributed, fault tolerant, and provides load balancing and logarithmic search performance while supporting both equality and range queries. Our theoretical analysis as well as experimental results, obtained both in a simulated environment and on PlanetLab, show the performance of our system.

Many structured peer-to-peer (P2P) systems have been proposed as distributed hash tables (DHTs) for fast and efficient lookup of queries. In this paper, we propose a novel technique for improving average lookup times in P2P systems by caching additional neighbor pointers based on peer access frequencies. In particular, we address the problem of each peer choosing the k best pointers to store (in addition to its index pointers) to minimize the average query lookup times. We focus on two popular P2P systems, namely Pastry and Chord: we exploit the inherent structure of these systems to develop efficient, scalable algorithms for optimally choosing the k additional pointers. Simulations with Chord and Pastry demonstrate that our algorithms are very effective in reducing the lookup times significantly. Our approach can be used in tandem with other techniques such as item caching and replication, and is particularly useful for applications such as name services in mobile environments or location services, where we can expect a low churn rate for peers and a relatively higher churn rate for items.

Peer-to-peer systems have emerged as a robust, scalable and decentralized way to share and publish data. In this paper, we propose P-Ring, a new P2P index structure that supports both equality and range queries. P-Ring is fault-tolerant, provides logarithmic search performance even for highly skewed data distributions and efficiently supports large sets of data items per peer. We experimentally evaluate P-Ring using both simulations and a real distributed deployment on PlanetLab, and we compare its performance with Skip Graphs, Online Balancing and Chord.

New and emerging P2P applications require sophisticated range query capability and also have strict requirements on query correctness, system availability and item availability. While there has been recent work on developing new P2P range indices, none of these indices guarantee correctness and availability. In this paper, we develop new techniques that can provably guarantee the correctness and availability of P2P range indices. We develop our techniques in the context of a general P2P indexing framework that can be instantiated with most P2P index structures from the literature. As a specific instantiation, we implement P-Ring, an existing P2P range index, and show how it can be extended to guarantee correctness and availability. We quantitatively evaluate our techniques using a real distributed implementation. 1

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We propose a new distributed, fault-tolerant peer-to-peer index structure called the P-tree. P-trees efficiently evaluate range queries in addition to equality queries.