OCD: obsessive consensus disorder (or repetitive consensus)

  • Authors:
  • Danny Dolev;Ezra N. Hoch

  • Affiliations:
  • Hebrew University, Jerusalem, Israel;Hebrew University, Jerusalem, Israel

  • Venue:
  • Proceedings of the twenty-seventh ACM symposium on Principles of distributed computing
  • Year:
  • 2008

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Abstract

Consider a distributed system S of sensors, where the goal is to continuously output an agreed reading. The input readings of non-faulty sensors may change over time; and some of the sensors may be faulty (Byzantine). Thus, the system is required to repeatedly perform consensus on the input values. This paper investigates the following question: assuming the input values of all the non-faulty sensors remain unchanged for a long period of time, what can be said about the agreed-upon output reading of the entire system? We prove that no system's output is stable, i.e. the faulty sensors can force a change of the output value at least once. We show that any system with binary input values can avoid changing its output more than once, thus matching the lower bound. For systems with multi-value inputs, we show that the output may change at most twice; when n=3f+1 this solution is shown to be tight. Moreover, the solutions we present are self-stabilizing.