PPT-Impossibility of Consensus in Asynchronous Systems (FLP)

Ali Ghodsi UC Berkeley KTH alig at csberkeleyedu Ali Ghodsi aligatcsberkeleyedu 2 Modified Model A correct node can always make a dummy transition. Sarangi Department of Computer Science Indian Institute of Technology New Delhi India Smruti R Sarangi Pastry 125 brPage 2br Synchronous Systems Asynchronous Systems Outline Synchronous Systems Physical Clocks Quartz Clocks Atomic Clocks GPS 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 Ali Ghodsi. alig@cs.berkeley.edu. Replicated State Machine (RSM). Distributed Systems 101. Fault-tolerance. . (partial, byzantine, recovery,...). Concurrency. (ordering, asynchrony, timing,...). Generic. 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 Ken Birman. Fall 2012. Consensus… a classic problem. Consensus abstraction underlies many distributed systems and protocols. N processes. They start execution with inputs.  {0,1}. Asynchronous, reliable network. Paxos. --- 1. Steve Ko. Computer Sciences and Engineering. University at Buffalo. Recap. NFS. Caching with write-through policy at close(). Stateless server. One power efficient design: FAWN. Embedded CPUs & Flash . async. and await. Synchronous vs. Asynchronous programming, Tasks, C# 4.5 features . async. and await. George Georgiev. Telerik. Corporation. www.telerik.com. . Technical Trainer. itgeorge.net. . Sophia Yakoubov. Joint work with Leo . Reyzin. 1. Outline. Motivation: Distributed PKI. Background: Accumulators. Our Contributions: Asynchronous Accumulators. Definition: verification works even if the accumulator and witness are out of synch. 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.. 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.. 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” Lecture 4. Andrew Or, Michael Freedman. RAFT slides heavily based on those from Diego Ongaro and John Ousterhout. Provide behavior of a single copy of object:. Read should return the most recent write. Byzantine Generals Problem. Solution with signed message. . A . signed message. satisfies all the conditions of oral message, plus . two extra conditions. Signature cannot be forged. Forged message are detected and discarded by loyal generals.. 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. .