Consensus In Asynchrony

TL;DR

This paper presents an event-based synchronization algorithm for deterministic fault-tolerant consensus in asynchronous systems, challenging the FLP impossibility result by analyzing assumptions and demonstrating practical feasibility.

Contribution

It introduces a new algorithm achieving consensus with safety and liveness in asynchronous systems, and provides a nuanced analysis of FLP assumptions affecting consensus impossibility.

Findings

Algorithm terminates with valid vector agreement

Identifies two types of agreements: data-independent and data-dependent

Experimental evidence questions the third FLP assumption

Abstract

We demonstrate sufficiency of events-based synchronisation for solving deterministic fault-tolerant consensus in asynchrony. Main result is an algorithm that terminates with valid vector agreement, hence operates with safety, liveness, and tolerance to one crash. Reconciling with the FLP impossibility result, we identified: i) existence of two types of agreements: data-independent and data-dependent; and ii) dependence of FLP theorem correctness on three implicit assumptions. Consensus impossibility with data-dependent agreement is contingent on two of them. The theorem-stated impossibility with every agreement type hinges entirely on the third. We provide experimental results showing that the third assumption has no evidence in support.