convergent-replicated-set

Convergent Replicated Set (CR-Set), a delta CRDT for unordered, duplicate-free collections.

• Try the demo
• Check the docs
• Read the specification

Compatibility

• Runtimes: Node >= 20, modern browsers, Bun, Deno, Cloudflare Workers, Edge Runtime.
• Module format: ESM + CommonJS.
• Required globals / APIs: EventTarget, CustomEvent, structuredClone.
• TypeScript: bundled types.

Goals

• Deterministic convergence of the live set projection under asynchronous gossip delivery.
• Content-addressed membership for unordered, duplicate-free values.
• Consistent behavior across Node, browsers, worker, and edge runtimes.
• Garbage collection possibility without breaking live-set convergence.
• Event-driven API.

Installation

npm install @sovereignbase/convergent-replicated-set
# or
pnpm add @sovereignbase/convergent-replicated-set
# or
yarn add @sovereignbase/convergent-replicated-set
# or
bun add @sovereignbase/convergent-replicated-set
# or
deno add jsr:@sovereignbase/convergent-replicated-set
# or
vlt install jsr:@sovereignbase/convergent-replicated-set

Usage

Copy-paste example

import { CRSet } from '@sovereignbase/convergent-replicated-set'

const alice = new CRSet<string>()
const bob = new CRSet<string>()

alice.addEventListener('delta', (event) => {
  bob.merge(event.detail)
})

alice.add('alpha')
alice.add('beta')
alice.add('alpha')

console.log(alice.size) // 2
console.log(bob.has('alpha')) // true
console.log(bob.values()) // ['alpha', 'beta']

Hydrating from a snapshot

import {
  CRSet,
  type CRSetSnapshot,
} from '@sovereignbase/convergent-replicated-set'

type Member = {
  id: string
  role: 'admin' | 'member'
}

const source = new CRSet<Member>()
let snapshot!: CRSetSnapshot<Member>

source.addEventListener(
  'snapshot',
  (event) => {
    snapshot = event.detail
  },
  { once: true }
)

source.add({ id: 'alice', role: 'admin' })
source.add({ id: 'bob', role: 'member' })
source.snapshot()

const restored = new CRSet<Member>(snapshot)

console.log(restored.size) // 2
console.log(restored.has({ id: 'alice', role: 'admin' })) // true

Event channels

import { CRSet } from '@sovereignbase/convergent-replicated-set'

const set = new CRSet<string>()

set.addEventListener('delta', (event) => {
  console.log('delta', event.detail)
})

set.addEventListener('change', (event) => {
  console.log('change', event.detail)
})

set.addEventListener('snapshot', (event) => {
  console.log('snapshot', event.detail)
})

set.addEventListener('ack', (event) => {
  console.log('ack', event.detail)
})

set.add('draft')
set.delete('draft')
set.snapshot()
set.acknowledge()

Iteration and JSON serialization

import { CRSet } from '@sovereignbase/convergent-replicated-set'

const set = new CRSet<string>()

set.add('red')
set.add('green')
set.add('blue')

const serialized = JSON.stringify(set)
const restored = new CRSet<string>(JSON.parse(serialized))

for (const value of set) {
  console.log(value)
}

set.forEach((value, target) => {
  console.log(value, target.size)
})

console.log(set.values())
console.log(restored.has('green')) // true

This example assumes your set values are JSON-compatible. For general structuredClone-compatible values such as Date, Map, or BigInt, persist snapshots with a structured-clone-capable store or an application-level codec instead of plain JSON.stringify / JSON.parse.

values(), for...of, and forEach() return detached copies of visible values. Mutating those returned values does not mutate the underlying replica state.

Acknowledgements and garbage collection

import { CRSet, type CRSetAck } from '@sovereignbase/convergent-replicated-set'

const alice = new CRSet<string>()
const bob = new CRSet<string>()
const frontiers = new Map<string, CRSetAck>()

alice.addEventListener('delta', (event) => {
  bob.merge(event.detail)
})

bob.addEventListener('delta', (event) => {
  alice.merge(event.detail)
})

alice.addEventListener('ack', (event) => {
  frontiers.set('alice', event.detail)
})

bob.addEventListener('ack', (event) => {
  frontiers.set('bob', event.detail)
})

alice.add('x')
alice.delete('x')

alice.acknowledge()
bob.acknowledge()

alice.garbageCollect([...frontiers.values()])
bob.garbageCollect([...frontiers.values()])

Runtime behavior

Validation and errors

Public mutations can throw CRSetError with stable error codes:

• VALUE_NOT_ENCODABLE
• VALUE_NOT_CLONEABLE

Ingress stays tolerant through the underlying CR-Map replication layer:

• duplicate identical additions are no-ops
• duplicate delete and merge payloads are idempotent
• stale or dominated incoming state does not break live-set convergence
• dominated incoming state may emit a reply delta

Safety and copying semantics

• Values are identified by the SHA-256 Base64URL digest of their canonical MessagePack encoding.
• Snapshots are serializable full-state payloads with values and tombstones.
• Deltas are serializable partial snapshot payloads with values and tombstones.
• change is a minimal value-keyed visible patch where deleted values map to undefined.
• toJSON() returns a detached serializable snapshot.
• JSON.stringify() and toString() are only reliable when set values are JSON-compatible.
• values(), for...of, and forEach() expose detached copies of visible values rather than mutable references into replica state.
• add(), has(), delete(), clear(), merge(), snapshot(), acknowledge(), and garbageCollect() all operate on the live set projection.

Convergence and compaction

• The convergence target is the visible set projection, not identical internal tombstone sets.
• Membership is content-addressed: structurally identical canonical MessagePack values resolve to the same set member.
• add() is idempotent when the value's content key is already visible.
• delete() removes the visible value identified by the value's current content key.
• Tombstones remain until acknowledgement frontiers make them safe to collect.
• Garbage collection compacts tombstoned history while preserving the converged live projection for replicas that later catch up from delta or snapshot state.

Tests

npm run test

Current status on Node v22.14.0 (win32 x64): npm run test passes.

• Unit: 14/14 CRSet core invariants passed.
• Integration: 17/17 replication and stress invariants passed.
• Module interop: ESM/CJS snapshots and deltas, root exports, and JSON-cloned snapshots passed.
• Coverage: 100% statements, branches, functions, and lines on built dist/**/*.js.
• End-to-end matrix passed: Node ESM/CJS, Bun ESM/CJS, Deno ESM, Cloudflare Workers ESM, Edge Runtime ESM, Chromium, Firefox, WebKit, mobile Chrome, and mobile Safari.

Benchmarks

npm run bench

Last measured on Node v22.14.0 (win32 x64):

group	scenario	n	ops	ms	ms/op	ops/sec
class	constructor / hydrate snapshot	5,000	250	17,511.69	70.05	14.28
class	has / primitive value	5,000	250	2.02	0.01	123,578.84
class	has / object value	5,000	250	2.92	0.01	85,683.93
class	has / falsy value	5,000	250	1.63	0.01	152,951.97
class	has / missing value	5,000	250	2.63	0.01	95,158.34
class	values()	5,000	250	8,841.84	35.37	28.27
class	iterator	5,000	2,500,000	7,869.60	0.00	317,677.98
class	forEach()	5,000	2,500,000	8,213.18	0.00	304,388.64
class	add / string	5,000	250	6.82	0.03	36,636.48
class	add / object	5,000	250	11.62	0.05	21,521.85
class	add / duplicate object	5,000	250	2.33	0.01	107,153.57
class	delete(value)	5,000	250	4.69	0.02	53,342.44
class	clear()	5,000	250	1,026.42	4.11	243.56
class	snapshot	5,000	250	7,950.54	31.80	31.44
class	acknowledge	5,000	250	678.65	2.71	368.38
class	garbage collect	5,000	250	157.49	0.63	1,587.36
class	merge ordered deltas	5,000	250	4.57	0.02	54,746.52
class	merge direct successor	5,000	250	4.73	0.02	52,831.78
class	merge shuffled gossip	5,000	250	8.87	0.04	28,172.82
class	merge stale conflict	5,000	250	5.42	0.02	46,103.35

License

Apache-2.0