A Formal Model for Eventual Consistency Semantics

Wide-area replicated systems are characterized by a conflict between performance, availability and consistency. As a consequence, “one-size-fits-all” approaches will inadequately address every situation. Therefore, there is a need for a formalism that can be used to express consistency requirements in a uniform way, as well as for new algorithms and techniques appropriate for the wide-area setting. This paper takes advantage of dependency relations between operations for improving the classic algorithm for eventual consistency and proposes a formal model used for reasoning about the correctness of the algorithm. The proposed algorithm reduces the number of undo operations when independence between operations can be exploited. The formal model allows us to describe and reason about replication and consistency semantics in a formal manner. The new algorithm provides good results when dependence relations between operations can be identified.