Fast Flexible Paxos: Relaxing Quorum Intersection for Fast Paxos

TL;DR

This paper proposes a relaxation of quorum intersection requirements in Fast Paxos, enabling smaller quorums and new tradeoffs between performance and fault-tolerance in distributed consensus.

Contribution

It introduces a relaxed quorum intersection model for Fast Paxos, reducing quorum sizes and expanding the design space for efficient, fault-tolerant consensus protocols.

Findings

Relaxed intersection requirements are safe for Fast Paxos.

Larger quorums are unnecessary for correctness.

New tradeoffs between performance and fault-tolerance are possible.

Abstract

Paxos, the de facto standard approach to solving distributed consensus, operates in two phases, each of which requires an intersecting quorum of nodes. Multi-Paxos reduces this to one phase by electing a leader but this leader is also a performance bottleneck. Fast Paxos bypasses the leader but has stronger quorum intersection requirements. In this paper we observe that Fast Paxos' intersection requirements can be safely relaxed, reducing to just one additional intersection requirement between phase-1 quorums and any pair of fast round phase-2 quorums. We thus find that the quorums used with Fast Paxos are larger than necessary, allowing alternative quorum systems to obtain new tradeoffs between performance and fault-tolerance.