The unbeatability of a consensus protocol, introduced by Halpern, Moses and Waarts in , 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 non-uniform 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.
KeywordsConsensus uniform consensus optimality knowledge
Unable to display preview. Download preview PDF.
- 1.Castañeda, A., Gonczarowski, Y.A., Moses, Y.: Brief announcement: Pareto-optimal solutions to consensus and set consensus. In: PODC, pp. 113–115 (2013)Google Scholar
- 2.Castañeda, A., Gonczarowski, Y.A., Moses, Y.: Unbeatable consensus (September 2014), http://arXiv.org
- 4.Coan, B.: A communication-efficient canonical form for fault-tolerant distributed protocols. In: Proc. 5th ACM Symp. on Principles of Distributed Computing, pp. 63–72 (1986)Google Scholar
- 6.Dolev, D., Strong, H.R.: Requirements for agreement in a distributed system. In: Schneider, H.J. (ed.) Distributed Data Bases, pp. 115–129. North-Holland (1982)Google Scholar
- 7.Dolev, D.: Beep protocols (personal communication)Google Scholar
- 10.Fagin, R., Halpern, J.Y., Moses, Y., Vardi, M.Y.: Reasoning about Knowledge. MIT Press (2003)Google Scholar
- 14.Halpern, J.Y., Moses, Y.: Knowledge and common knowledge in a distributed environment. Journal of the ACM 37(3), 549–587 (1990), a preliminary version appeared in PODC (1984)Google Scholar
- 16.Herlihy, M., Moses, Y., Tuttle, M.R.: Transforming worst-case optimal solutions for simultaneous tasks into all-case optimal solutions. In: PODC, pp. 231–238 (2011)Google Scholar
- 19.Moses, Y.: Knowledge and Distributed Coordination (in preparation)Google Scholar
- 21.Raynal, M.: Optimal early stopping uniform consensus in synchronous systems with process omission failures. In: SPAA, pp. 302–310. ACM Press (2004)Google Scholar