replicatable

Library of CRDTs (Conflict-free replicated data types) implemented in TypeScript

Implemented Types

Convergent replicated data types (CvRDTs), state based

CvRDTs are replicated by sending the full local state to other replicas and calling the commutative, associative and idempotent merge function.

GCounter

The GCounter (Grow-only-Counter) is a counter that can only be incremented on n nodes. Each node needs to be assigned a cluster-wide unique ID.

import { GCounter } from "replicatable";
const firstCounter = new GCounter('first');
firstCounter.increment(3);

const secondCounter = new GCounter('second');
secondCounter.increment(7);

firstCounter.merge(secondCounter);

console.log(firstCounter.value); // 10

PNCounter

The PNCounter (Positive-Negative-Counter) combines two GCounter instances, one for increments and one for decrements.

import { PNCounter } from "replicatable";
const firstCounter = new PNCounter('first');
firstCounter.decrement(4);

const secondCounter = new PNCounter('second');
secondCounter.increment(6);

firstCounter.merge(secondCounter);

console.log(firstCounter.value); // 2

GSet

The GSet (Grow-only-Set) is a set that only allows adds.

import { GSet } from "replicatable";
const firstSet = new GSet();
firstSet.add('foo');

const secondSet = new GSet();
secondSet.add('bar');

firstSet.merge(secondSet);
console.log(firstSet) // Set(['foo', 'bar'])

TwoPhaseSet

The TwoPhaseSet is a set that only allows elements to be added and removed. It combines two GSets for additins and removals.

import { TwoPhaseSet } from "replicatable";
const firstSet = new TwoPhaseSet();
firstSet.add('foo');
firstSet.add('baz');

const secondSet = new TwoPhaseSet();
secondSet.add('bar');
secondSet.remove('baz');

firstSet.merge(secondSet);
console.log(firstSet) // Set(['foo', 'bar'])

Prior Work

• barend-erasmus/pangolin
• orbitdb/crdts
• ljwagerfield/crdt
• pfrazee/crdt_notes