Realtime: Multiplayer Edition

Summary

Supabase announces the general availability of Realtime’s multiplayer features, Broadcast and Presence, alongside a new channel-based architecture and supabase-js support. Realtime originally used Postgres logical replication, rather than LISTEN/NOTIFY, to avoid the latter’s 8,000-byte payload limit and the latency of querying each change from the database. In the new design, Channels act as rooms that support ephemeral publisher/subscriber Broadcast messages, shared Presence state, and Postgres change events; Presence uses Phoenix Tracker, a delta-based CRDT, for eventually consistent synchronization and removes disconnected users automatically. Realtime now runs as a distributed Elixir and Phoenix cluster on Fly, with clients connecting to the nearest node and nodes communicating across a backbone network to improve connection speed, stability, and latency. Free-plan active projects and projects created from August 18 have access, while other projects are scheduled for migration over the following weeks.

Takeaways

1. 1

   Broadcast bypasses the database, making it suitable for real-time data such as cursor positions that previously could add latency and degrade database performance when sent through Postgres.

2. 2

   Presence persists shared channel state for new joiners, synchronizes it eventually and conflict-free, and automatically removes a user’s state after an unexpected disconnect.

3. 3

   The new Realtime deployment distributes servers globally, routes clients to the nearest node, and uses inter-node communication to improve connection speed, stability, and latency.