A framework for establishing Strong Eventual Consistency for Conflict-free Replicated Datatypes
Victor B. F. Gomes, Martin Kleppmann, Dominic P. Mulligan, and Alastair R. Beresford
Archive of Formal Proofs,
July 2017.
Abstract
In this work, we focus on the correctness of Conflict-free Replicated Data Types (CRDTs), a class of
algorithm that provides strong eventual consistency guarantees for replicated data. We develop
a modular and reusable framework for verifying the correctness of CRDT algorithms. We avoid
correctness issues that have dogged previous mechanised proofs in this area by including a network
model in our formalisation, and proving that our theorems hold in all possible network behaviours.
Our axiomatic network model is a standard abstraction that accurately reflects the behaviour of
real-world computer networks. Moreover, we identify an abstract convergence theorem, a property of
order relations, which provides a formal definition of strong eventual consistency. We then obtain
the first machine-checked correctness theorems for three concrete CRDTs: the Replicated Growable
Array, the Observed-Remove Set, and an Increment-Decrement Counter.