CASPaxos: Replicated State Machines without logs

Abstract

CASPaxos is a wait-free, linearizable, multi-writer multi-reader register in unreliable, asynchronous networks supporting arbitrary update operations including compare-and-set (CAS). The register acts as a replicated state machine providing an interface for changing its value by applying an arbitrary user-provided function (a command). Unlike Multi-Paxos and Raft which replicate the log of commands, CASPaxos replicates state, thus avoiding associated complexity, reducing write amplification, increasing concurrency of disk operations and hardware utilization. The paper describes CASPaxos, proves its safety properties and evaluates the characteristics of a CASPaxos-based prototype of key-value storage.