Antipaxos: Taking interactive consistency to the next level

Abstract

Classical Paxos-like consensus protocols limit system scalability due to a single leader and the inability to process conflicting proposals in parallel. We introduce a novel agreement protocol, called Antipaxos, that instead reaches agreement on a collection of proposals using an efficient leaderless fast path when the environment is synchronous and failure-free, and falls back on a more elaborate slow path to handle other cases. We first specify the main safety property of Antipaxos by formalizing a new agreement problem called k-Interactive Consistency (k-IC). Then, we present a solution to this problem in the Byzantine failure model. We prove safety and liveness, and also present an experimental performance evaluation in the Amazon cloud. Our experiments show that Antipaxos achieves several-fold higher failure-free peak throughput than Mir-BFT. The inherent efficiency of our approach stems from the low message complexity of the fast path: agreement on n batches of conflict-prone proposals is achieved using only $\Theta \left(n^2\right)$ messages in one consensus cycle, or $\Theta \left(n\right)$ amortized messages per batch.