A Preliminary Model of Coordination-free Consistency
Shulu Li, Edward A. Lee
TL;DR
This paper proposes a simple distributed computation model that separates coordination from computation and formally defines strong eventual consistency, consistency, coordination-free, and monotonicity. It proves a necessary-and-sufficient condition for SEC via an associative, commutative, and idempotent merge and provides a distributed-computation interpretation and proof of the CALM theorem. The results show that monotonic problems admit coordination-free implementations and that coordination-free implementations imply monotonicity, offering a principled lens for when global coordination is avoidable. The framework connects CRDT-inspired ideas with CALM, enabling reasoning about availability and timing through concepts like partitioning and Scott continuity. Overall, the work supplies a theoretical foundation for deciding when coordination-free guarantees are possible and guides design of distributed systems with predictable consistency properties.
Abstract
Building consistent distributed systems has largely depended on complex coordination strategies that are not only tricky to implement, but also take a toll on performance as they require nodes to wait for coordination messages. In this paper, we explore the conditions under which no coordination is required to guarantee consistency. We present a simple and succinct theoretical model for distributed computation that separates coordination from computation. The main contribution of this work is mathematically defining concepts in distributed computing such as strong eventual consistency, consistency, consistent under partition, confluence, coordination-free, and monotonicity. Based on these definitions, we prove necessary and sufficient conditions for strong eventual consistency and give a proof of the CALM theorem from a distributed computation perspective.