Distributed Systems also: Conflict-free Replicated Data Type

CRDT

A data type whose merges are commutative, associative, idempotent.

In plain terms

Strongly eventual consistency without coordination. The math behind every collaborative editor (Yjs, Automerge).

Origin

Marc Shapiro, Nuno Preguiça, Carlos Baquero, and Marek Zawirski formalised CRDTs in a 2011 INRIA technical report. The underlying ideas (commutative replicated structures) appeared earlier in Operational Transformation research, but CRDTs gave them a clean mathematical footing.

Where it shows up in production

Figma Multiplayer cursors and edits converge via a CRDT-style structure; no central lock.
Redis CRDT-based active-active replication in Enterprise/Cloud versions.
Automerge & Yjs The dominant open-source CRDT libraries; Yjs powers Notion-like collaborative editors.

On Semicolony

Simulator crdt Paper papers

Sources & further reading

Paper Shapiro et al. — A Comprehensive Study of Convergent and Commutative Replicated Data Types (2011)
Docs crdt.tech — annotated catalogue
Talk Martin Kleppmann — CRDTs: The Hard Parts (talk)

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