Kevin Jahns

State Synchronization for Collaborative Apps

Realtime & Automatic Conflict Resolution

Replicated Data Types (RDT)

  • Abstraction for storing application state
  • Optimistic Replication
  • Observable

Replicated Data Types (RDT)

  • Abstraction for storing application state
  • Optimistic Replication
  • Observable

RDT Example: Yjs

import * as Y from 'yjs'

const ydoc = new Y.Doc()

const webrtcProvider = new WebrtcProvider('room-name', ydoc, { password: 'optional-room-password' })
// const websocketProvider = new WebsocketProvider(url, 'room-name', ydoc)
// const matrixProvider = new MatrixProvider(ydoc, matrixClient, {type: "alias",alias: "matrix-room-alias"});

const ymap = ydoc.getMap('map')
const yarray = ydoc.getArray('array')
const ytext = ydoc.getText('text')
const yxml = ydoc.getXmlElement('el')

ymap.observe(event => {
  console.log(event.changes.keys) // { "my key": { action: 'add', oldValue: undefined } }
})

ymap.set('my key', 'new value')

Lexical Editor by Meta is built on-top of Yjs

Lexical Editor

SyncedStore

SyncedStore

import React from "react";
import { useSyncedStore } from "@syncedstore/react";
import { store } from "./store";

export default function App() {
  const state = useSyncedStore(store);

  return (
    <div>
      <p>Todo items:</p>
      <ul>
        {state.todos.map((todo, i) => (
          <li key={i} style={{ textDecoration: todo.completed ? "line-through" : "" }}>
            <label>
              <input type="checkbox" checked={todo.completed} onClick={() => (todo.completed = !todo.completed)} />
              {todo.title}
            </label>
          </li>
        ))}
      </ul>
      <input
        onKeyPress={(event) => {
          if (event.key === "Enter") {
            state.todos.push({ completed: false, title: event.target.value });
            target.value = "";
          }
        }}
      />
    </div>
  );
}

SyncedStore

RDT: Business appeal

  • Quick prototyping
  • Realtime & collaborative
  • Little setup
  • No backend logic
  • (Pay as you go)
  • (snapshots)
  • (offline support)

Yjs is a Conflict-free RDT (CRDT)

Operations are commutative, idempotent, and associative

 

⇒ o1 • o2 • o3 == o3 • o2 • o1 • o2

Yjs Ecosystem

  • y-webrtc
  • y-websocket
  • hocuspocus
  • liveblocks
  • y-sweet
  • yrs-warp
  • matrix-crdt
  • ..
  • y-prosemirror
  • y-quill
  • y-codemirror
  • y-ace
  • y-monaco
  • lexical
  • ...

Editor Bindings

Connectors

Persistence

  • y-indexeddb
  • y-leveldb
  • ystream

Y CRDT

Yjs ported to different programming languages

Work of Bartosz Sypytkowski and many others

Ycs

How I work

  • Consulting
  • Organizing OSS work
  • Sponsors

Control

Control

Image is CC: https://www.flickr.com/photos/nossreh/10987353554

• Who "owns" data

• Who performs

  conflict resolution?

Centrality

source: https://www.printablee.com/post_50-states-printable-out-maps_185196/

Centrality

Why can't my favorite file syncing service sync directly to my phone. Instead I first upload to the US, and then sync back

Centrality / Central Place of Control

+ Easier to coordinate

 

- No direct sync

- No sync if service is not reachable

- Harder to scale

Conflict-free RDTs: CRDTs

Alternatively: Coordination-free RDT
                         I.e. RDTs that don't require centrality

Shared Control

• Users "own" data

• Everyone performs

  conflict resolution

Sync Peer-to-Peer

Sync on the Edge

Make it Available Offline

y-redis

  • Infinitely scalable backend for y-websocket
  • Distributes updates efficiently using redis streams
  • Stores documents in S3 or Postgres
  • Only syncs a document at a time

Ystream

  • A database for CRDTs, based on LMDB
  • Sync millions of documents in seconds
  • Revision control for humans
  • Users own their data

Current focus

twitter.com/kevin_jahns

State Synchronization - reaktor presentation

By Kevin Jahns

State Synchronization - reaktor presentation

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