PPT-Impossibility of Consensus

Ken Birman Fall 2012 Consensus a classic problem Consensus abstraction underlies many distributed systems and protocols N processes They start execution with inputs 01 Asynchronous reliable network. FISCHER Yale University New Haven Connecticut NANCY A LYNCH Massachusetts Institute of Technology Cambridge Massachusetts AND MICHAEL S PATERSON University of Warwick Coventry England Abstract The consensus problem involves an asynchronous system of Yale University, New Haven, Connecticut NANCY A. LYNCH Massachusetts Institute of Technology, Cambridge, Massachusetts AND MICHAEL S. PATERSON University of Warwick, Coventry, England Abstract. I Auxiliary Input or a Universal Simulator. Nir. . Bitansky. . Ran Canetti. Henry Cohn. Shafi. . Goldwasser. Yael . Tauman-Kalai. . Omer Paneth. Alon. Rosen. Program Obfuscation. Obfuscated program. Nir. . Bitansky. and Omer . Paneth. Program Obfuscation. Compute .  .  .  . Program Obfuscation.  .  . Program Obfuscation. Sign email . with . If . starts with “omer@bu.edu”.  .  .  . Dennis Shasha (following Lynch, Fischer, Patterson). Failure Model. Processes can fail-stop (but that is all; no fail traitorous).. Communication is two-way.. Messages can be dropped or take an arbitrarily long time.. A Tool for Teams. Sister Singers Festival. July 25, 2014. Presenter: Mindy Taylor. Session Overview. Become familiar with a group process tool called Consensus Validation. Learn the steps in doing Consensus Validation. A Tool for Teams. GALA Leadership Symposium. October 11, 2013. Presenter: Mindy Taylor. Session Overview. Become familiar with a group process tool called Consensus Validation. Learn the steps in doing Consensus Validation. When you can’t agree to disagree. Consensus. Why do applications need consensus?. What does it mean to have consensus?. Consensus = consistency. Assumptions. Processes can choose values. Run at arbitrary speeds. Failure Model. Processes can fail-stop (but that is all; no fail traitorous).. Communication is two-way.. Messages can be dropped or take an arbitrarily long time.. To show: no algorithm can guarantee to solve consensus in the face of fail-stop processes and unlimited message delays.. Nir. . Bitansky. and Omer . Paneth. Program Obfuscation. Compute .  .  .  . Program Obfuscation.  .  . Program Obfuscation. Sign email . with . If . starts with “omer@bu.edu”.  .  .  . Consensus I FLP Impossibility, Paxos COS 418: Distributed Systems Lecture 7 Michael Freedman 2 Recall our 2PC commit problem C  TC: “go!” TC  A, B: “prepare!” A, B  P: “yes” By,. Michael . J.Fischer. Nancy A. Lynch. Michael . S.Paterson. What is . Consensus Problem?. Consensus . is the task of getting all processes in a group to agree on some specific value based on the votes of each processes. . for Replicated Logs. Diego Ongaro and John Ousterhout. Stanford University. Replicated log => . replicated state . machine. All servers execute same commands in same . order. Consensus module ensures proper log replication. Ali . Ghodsi. – . UC Berkeley / KTH. alig. (. at. ). cs.berkeley.edu. Ali Ghodsi, alig(at)cs.berkeley.edu. 2. Modified Model. A . correct. . node can always make a . “. dummy. ”. transition.