Consensus In Asynchrony
Ivan Klianev
TL;DR
This paper tackles deterministic fault-tolerant consensus in total asynchrony by introducing an events-based synchronization approach and a vector-agreement algorithm that terminates with a vector of initial inputs for at least $n-1$ correct processes. It argues that FLP's impossibility result rests on hidden, model-dependent assumptions and distinguishes data-dependent (binary) from data-independent (vector) agreements, showing that vector consensus can be achieved despite asynchrony and one crash. The authors provide both analytic proofs and physical experiments to support the claim that vector consensus is feasible and that the apparent impossibility of binary agreement is not universal but tied to how tie states are interpreted. The work thus broadens the theoretical landscape, suggesting deterministic fault-tolerant consensus in total asynchrony is possible under data-independent vector agreement and has implications for real-world distributed systems operating in partially synchronous environments.
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.