>Cursor is powered by a single-box Postgres instance Why wouldn't it? The resources needed to run the backend of Cursor come from the compute for the AI models. Updating someone's quota in a database every few minutes is not going to be causing issues.
In the nosql era the idea that you could run even the basics for a >1m user SaaS platform on an ordinary, free, single-node transactional SQL database would have been considered nuts.
Today big boxes are big. Really big. Stuff like 128 cores, 1TB RAM, and dozens of terabytes of incredibly fast RAIDed flash storage is available out there.
They're also more reliable than they used to be. Hardware still fails of course, but it doesn't fail as often as OG spinning disk did.