Supabase Realtime

Realtime offers three features over one WebSocket connection. Broadcast sends low-latency messages between clients, such as chat or cursor positions. Presence tracks who is online in a channel. Postgres Changes listens for inserts, updates and deletes in chosen tables and pushes them to subscribers, checking row level security for each one.

It is an Elixir server that reads database changes through Postgres logical replication. For busy apps Supabase recommends Broadcast, sent from database triggers, over Postgres Changes, because it scales better and gives finer control over who receives what. Usage counts towards each plan's quota of concurrent connections and messages.