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Conflict-free replicated data types to archive eventual consistency

1 min read

Hola persona grandiosa,

after last weeks topic on the CAP theorem, this week is a lot more practical. A conflict-free replicated data type (CRDT) helps you build a distributed system where all nodes converge to the same state. I challenge you to read the paper and build a minimal distributed system with a CRDT. Feel free to share your results in the Telegram group, we are happy to learn what you learned.


Replicating data under Eventual Consistency (EC) allows any replica to accept updates without remote synchronization. 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 sufficient 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 formalizes 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.

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With much love,

Simon Frey