Revisiting the paxos algorithm

Abstract

This paper develops a new I/O automaton model called the Clock General Timed Automaton (Clock GTA) model. The Clock GTA is based on the General Timed Automaton (GTA) of Lynch and Vaandrager. The Clock GTA provides a systematic way of describing timingbased systems in which there is a notion of “normal” timing behavior, but that do not necessarily always exhibit this “normal” behavior. It can be used for practical time performance analysis based on the stabilization of the physical system. We use the Clock GTA automaton to model, verify and analyze the PAXOS algorithm. The PAXOS algorithm is an efficient and highly fault-tolerant algorithm, devised by Lamport, for reaching consensus in a distributed system. Although it appears to be practical, it is not widely known or understood. This paper contains a new presentation of the PAXOS algorithm, based on a formal decomposition into several interacting components. It also contains a correctness proof and a time performance and fault-tolerance analysis.