by asonge

asonge / loom

A CRDT library with δ-CRDT support.

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Loom is a set of basic CRDT's that are designed to be composable and extensible. We include support for delta-CRDT's (δ-CRDT's) where it makes sense.


In order to combat issues with large objects, δ-CRDT's are supported for some datatypes. You can extract deltas from delta-CRDT's, and periodically clear them out from your datastructures to reduce memory constraints.

What the heck is a CRDT?

Conflict-free, Coordination-free, Commutative, or Convergent datatypes, CRDT's are usually formally described as "join semi-lattices". Mathematical jargon aside, CRDT's track causality for modifications to your data. Because of this, time becomes less relevant, and coordination becomes unnecessary to get accurate values for your data.

Can you give me an example of one?

I will have a simple explanation here for a basic gcounter and a pncounter.

For now, I can simply point you to the GCounter code in here.

Where can I learn more?

  • Strong Eventual Consistency and Conflict-free Replicated Data Types
    • A good introduction to the concept of CRDTs: http://research.microsoft.com/apps/video/default.aspx?id=153540&r=1
  • A comprehensive study of Convergent and Commutative Replicated Data Types
    • A survey with references for several popular CRDTs: http://hal.inria.fr/docs/00/55/55/88/PDF/techreport.pdf
  • Efficient State-based CRDTs by Delta-Mutation
    • Talk: https://www.youtube.com/watch?v=y_ewFP-lgyM
    • Paper: http://arxiv.org/pdf/1410.2803v1.pdf

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