🤖 AI Summary
This work investigates whether coordination is inherently required by specifications in distributed systems, independent of any particular protocol or implementation. Operating within the asynchronous message-passing model, it introduces a semantic characterization of coordination requirements based on the monotonicity of history extensions, leveraging Lamport’s happens-before partial order and the observable outcomes defined by the specification. Notably, this approach requires no assumptions about programming languages or protocols. The framework unifies and explains several foundational results—including CAP, CALM, snapshot consistency, and transaction isolation—by precisely delineating the boundary between specifications that can be implemented without coordination and those that fundamentally require it, thereby offering a cohesive theoretical foundation for distributed computing.
📝 Abstract
When is coordination intrinsically required by a distributed specification, rather than imposed by a particular protocol or implementation strategy? We give a general answer using minimal assumptions. In an asynchronous message-passing model, we show that a specification admits a coordination-free implementation if and only if it is monotone with respect to history extension under an appropriate order on observable outcomes. This Coordination Criterion is stated directly over Lamport histories -- partially ordered executions under happens-before -- and specification-defined observable outcomes, without assuming any particular programming language, object implementation, or protocol structure. It yields a sharp boundary between specifications that can be implemented without coordination and those for which coordination is unavoidable. The criterion provides a uniform explanation for a range of classical results, including CAP-style impossibility, CALM-style coordination-freedom, agreement and snapshot tasks, transactional isolation levels, and invariant confluence -- all instances of the same underlying semantic phenomenon.