Object Oriented Consensus

We suggest a template that reveals the structure of many consensus algorithms as a generic procedure. The template builds on an extension of the well known adopt-commit protocol which we call vacillateadopt-commit and on an extension of Aspnes’ conciliator protocol, which we call reconciliator. The consensus algorithm template works in rounds in each of which the vacillate-adopt-commit is invoked and if necessary also the reconciliator is called upon. The vacillate-adopt-commit object observes the processors preferences and suggest a preference output with a measure of confidence (vacillate, adopt or commit) on the preference. The reconciliator, is used when there is no overall clear agreement, to ensure termination. To show that our template correctly captures a natural structure of consensus algorithms we put three well known algorithms within our template: The Phase King Byzantine algorithm, the BenOr randomized algorithm and the Paxos algorithm. We analyze and compare our template based on vacillate-adopt-commit and reconciliator objects to previous work [1, 2], suggesting a decomposition of consensus based on adopt-commit and conciliator objects. We claim that the three return values of vacillate-adopt-commit more accurately describe existing algorithms. Submitted as a regular paper. This is a student paper (Danny Vainstein and Edo Cohen are full-time M.Sc. students). ∗School of Computer Science, Tel-Aviv University. E-mails: [email protected], [email protected], [email protected] †School of Computer Science, Yale University. E-mail: [email protected]