Supabase Realtime Deep Dive — Postgres Changes, Broadcast, and Presence

Supabase Realtime gives you WebSocket-based push for three distinct use cases. Picking the wrong subsystem wastes messages and adds complexity, so this guide covers all three with Flutter code you can drop straight into production.

The Three Subsystems at a Glance

Feature Best for Persisted? Scale concern

Postgres Changes DB row events Yes — in PostgreSQL Messages/month

Broadcast Ephemeral signals No — fire-and-forget Messages/month

Presence Online state sync No — auto-clean on disconnect Presence events

Project Setup

# pubspec.yaml dependencies : supabase_flutter : ^2.5.0

Enter fullscreen mode

Exit fullscreen mode

// main.dart import 'package:supabase_flutter/supabase_flutter.dart' ;

Future < void > main () async { WidgetsFlutterBinding . ensureInitialized (); await Supabase . initialize ( url: const String . fromEnvironment ( 'SUPABASE_URL' ), anonKey: const String .…