A case for associative peer to peer overlays

The success of a P2P file-sharing network highly depends on the scalability and versatility of its search mechanism. Two particularly desirable search features are scope (ability to find infrequent items) and support for partial-match queries (queries that contain typos or include a subset of keywords). While centralized-index architectures (such as Napster) can support both these features, existing decentralized architectures seem to support at most one: prevailing protocols (such as Gnutella and FastTrack) support partial-match queries, but since search is unrelated to the query, they have limited scope. Distributed Hash Tables (such as CAN and CHORD) constitute another class of P2P architectures promoted by the research community. DHTs couple index location with the item's hash value and are able to provide scope but can not effectively support partial-match queries; another hurdle in DHT deployment is their tight control the overlay structure and data placement which makes them more sensitive to failures. Associative overlays are a new class of decentralized P2P architectures. They are designed as a collection of unstructured P2P networks (based on popular architectures such as gnutella or FastTrack), and the design retains many of their appealing properties including support for partial match queries, and relative resilience to peer failures. Yet, the search process is orders of magnitude more effective in locating rare items. Our design exploits associations inherent in human selections to steer the search process to peers that are more likely to have an answer to the query.