cachapa/crdt

Dart implementation of Conflict-free Replicated Data Types (CRDTs).

This project is heavily influenced by James Long's talk CRTDs for Mortals and includes a Dart-native implementation of Hybrid Local Clocks (HLC) based on the paper Logical Physical Clocks and Consistent Snapshots in Globally Distributed Databases (pdf).

It has minimal external dependencies, so it should run anywhere where Dart runs, which is pretty much everywhere.

The Crdt class implements CRDT conflict resolution and serves as a storage-agnostic interface for specific implementations. Als included with this package is MapCrdt, an ephemeral implementation using Dart HashMaps.

Other implementations include (so far):

• hive_crdt, a no-sql implementation using Hive as persistent storage.
• sql_crdt, an abstract implementation for using relational databases as a data storage backend.
• sqlite_crdt, an implementation using Sqlite for storage, useful for mobile or small projects.
• postgres_crdt, a sql_crdt that benefits from PostgreSQL's performance and scalability intended for backend applications.

See also crdt_sync, a turnkey approach for real-time network synchronization of Crdt nodes.

Usage

The simplest way to experiment with this package is to use the provided MapCrdt implementation:

import 'package:crdt/map_crdt.dart';

void main() {
  var crdt1 = MapCrdt(['table']);
  var crdt2 = MapCrdt(['table']);

  print('Inserting 2 records in crdt1…');
  crdt1.put('table', 'a', 1);
  crdt1.put('table', 'b', 1);

  print('crdt1: ${crdt1.getMap('table')}');

  print('\nInserting a conflicting record in crdt2…');
  crdt2.put('table', 'a', 2);

  print('crdt2: ${crdt2.getMap('table')}');

  print('\nMerging crdt2 into crdt1…');
  crdt1.merge(crdt2.getChangeset());

  print('crdt1: ${crdt1.getMap('table')}');
}

Implementations

crdt is currently helping build local-first experiences for:

• Libra a weigh management app with 1M+ installs.
• tudo an open-source simple to-do app + backend.

Are you using this package in your project? Let me know!

Features and bugs

Please file feature requests and bugs at the issue tracker.