Unfiltered Realtime subscription broadcasts every mutation

What it is

A Realtime subscription listens to event: '*' on a table with no filter key.

Why it matters

Every insert, update, and delete on that table is broadcast to every subscriber. Message volume becomes writes multiplied by connected clients, which is a cost curve that bends sharply the moment the product works.

How to fix it

Add a row-level filter so each client only receives what it displays, and subscribe to the specific events you handle rather than *. Filtering server-side is also a privacy control, not just a cost one.