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Clique: A transparent, Peer-to-Peer collaborative file sharing system
Richard, Bruno; Nioclais Mac, Donal; Chalon, Denis
Keyword(s): peer-to-peer; groupware; file system; replication; optimistic reconciliation
Abstract: Clique is a HP Labs Grenoble project. The goal is to develop a novel peer-to-peer, server-less distributed file system based on optimistic replication algorithms, which transparently integrates into users' native file systems. Some properties of the Clique system are epidemic replication, a no lost updates consistency model and conflict management, as well as disconnected operation and replica convergence. These properties ensure that updates done by any peer of the group will never be lost, and also that they will converge on all the group member machines. The system is well adapted to highly disconnected environments, network partitions, and variable join/leave rates. Even under adverse connectivity conditions, over time, assuming intermittent point-to-point connectivity between each peer and at least one other peer in the group, the local file system view at each node converges towards a consistent global view. The reconciliation protocol used is stateless and has no notion of group membership, in order to achieve a linear worst-case scalability in the order of N, the number of peers in the network. A lower layer protocol has been developed, which enables one-to-all communications by taking advantage of IP Multicast augmented with network load management and a priority mechanism ensuring liveness of the higher layers of the protocol.
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