Replicating data under Eventual Consistency (EC) allows
any replica to accept updates without remote synchronisation. This ensures performance and scalability in large-scale distributed systems (e.g.,
clouds). However, published EC approaches are ad-hoc and error-prone.
Under a formal Strong Eventual Consistency (SEC) model, we study suf-
ficient conditions for convergence. A data type that satisfies these conditions is called a Conflict-free Replicated Data Type (CRDT). Replicas
of any CRDT are guaranteed to converge in a self-stabilising manner,
despite any number of failures. This paper formalises two popular approaches (state- and operation-based) and their relevant sufficient conditions. We study a number of useful CRDTs, such as sets with clean
semantics, supporting both add and remove operations, and consider in
depth the more complex Graph data type. CRDT types can be composed
to develop large-scale distributed applications, and have interesting theoretical properties.
Springer-Verlag
Marc Shapiro,
Nuno Preguiça, Carlos Baquero,
Marek Zawirski
