Arpeggio: Metadata Indexing in a Structured Peer-to-Peer Network

Peer-to-peer networks require an efficient means for performing searches for files by metadata keywords. Unfortunately, current methods usually sacrifice either scalability or recall. Arpeggio is a peer-to-peer file-sharing network that uses the Chord lookup primitive as a basis for constructing distributed keyword-set index, augmented with index-side filtering, to address this problem. We introduce index gateways, a technique for minimizing index maintenance overhead. Arpeggio also includes a content distribution system for finding source peers for a file; we present a novel system that uses Chord subrings to track live source peers without the cost of inserting the data itself into the network, and supports postfetching: using information in the index to improve the availability of rare files. The result is a system that provides efficient query operations with the scalability and reliability advantages of full decentralization. We use analysis and simulation results to show that our indexing system has reasonable storage and bandwidth costs, and improves load distribution.