Problem
Implement a change feed: clients subscribe to a table (with an optional filter) and receive insert/update/delete events as rows change, backed by Postgres logical replication (Supabase Realtime).
Requirements
subscribe(table, filter) returns a stream of change events for matching rows.- Deliver inserts, updates, and deletes; fan out only the changes a subscription matches.
Areas to design
- Sourcing changes from the database (logical replication / WAL) rather than polling.
- Matching each change against active subscriptions and filters efficiently.
- Back-pressure and slow consumers; ordering and at-least-once vs exactly-once delivery.
Example
- subscribe("orders", status='paid') → a stream emitting only paid-order changes.