Unbeatable consensus

The unbeatability of a consensus protocol, introduced by Halpern, Moses and Waarts in [14], is a stronger notion of optimality than the accepted notion of early stopping protocols. Using a novel knowledge-based analysis, this paper derives the first practical unbeatable consensus protocols in the literature, for the standard synchronous message-passing model with crash failures. These protocols strictly dominate the best known protocols for uniform and for nonuniform consensus, in some case beating them by a large margin. The analysis provides a new understanding of the logical structure of consensus, and of the distinction between uniform and nonuniform consensus. Finally, the first (early stopping and) unbeatable protocol that treats decision values “fairly” is presented. All of these protocols have very concise descriptions, and are shown to be efficiently implementable.

[1]  Idit Keidar,et al.  A simple proof of the uniform consensus synchronous lower bound , 2003, Inf. Process. Lett..

[2]  Yoram Moses,et al.  Brief announcement: pareto optimal solutions to consensus and set consensus , 2013, PODC '13.

[3]  Joseph Y. Halpern,et al.  A characterization of eventual Byzantine agreement , 1990, PODC '90.

[4]  Danny Dolev,et al.  Requirements for Agreement in a Distributed System , 1982, DDB.

[5]  Nancy A. Lynch,et al.  Impossibility of distributed consensus with one faulty process , 1985, JACM.

[6]  Leslie Lamport,et al.  Reaching Agreement in the Presence of Faults , 1980, JACM.

[7]  Maurice Herlihy,et al.  Transforming worst-case optimal solutions for simultaneous tasks into all-case optimal solutions , 2011, PODC '11.

[8]  Rachid Guerraoui,et al.  The Time-Complexity of Local Decision in Distributed Agreement , 2007, SIAM J. Comput..

[9]  Nancy A. Lynch,et al.  Impossibility of distributed consensus with one faulty process , 1983, PODS '83.

[10]  B. Simons,et al.  Fault-Tolerant Distributed Computing , 1990, Lecture Notes in Computer Science.

[11]  Ronald Fagin,et al.  Reasoning about knowledge , 1995 .

[12]  Yoram Moses,et al.  Knowledge and Common Knowledge in a Byzantine Environment I: Crash Failures , 1986, TARK.

[13]  Brian A. Coan,et al.  A communication-efficient canonical form for fault-tolerant distributed protocols , 1986, PODC '86.

[14]  Joseph Y. Halpern,et al.  Knowledge and common knowledge in a distributed environment , 1984, JACM.

[15]  André Schiper,et al.  Uniform consensus is harder than consensus , 2004, J. Algorithms.

[16]  Yoram Moses,et al.  Programming simultaneous actions using common knowledge , 1987, Algorithmica.

[17]  Vassos Hadzilacos,et al.  On the Relationship Between the Atomic Commitment and Consensus Problems , 1990, Fault-Tolerant Distributed Computing.

[18]  Danny Dolev,et al.  Early stopping in Byzantine agreement , 1990, JACM.

[19]  Rachid Guerraoui,et al.  The Complexity of Early Deciding Set Agreement , 2011, SIAM J. Comput..

[20]  Michel Raynal,et al.  Optimal early stopping uniform consensus in synchronous systems with process omission failures , 2004, SPAA '04.

[21]  Jiannong Cao,et al.  A bivalency proof of the lower bound for uniform consensus , 2005, Inf. Process. Lett..