Ah, this is interesting: so Postgres is effectively a 'backend' for you, in much the same way that e.g. InnoDB is a backend for MySQL[0]?

And you - or hypothetically the end user - could change the backend, e.g. to Cockroach for better horizontal scalability, while trusting that EdgeDB will only rely on Postgres's public API at least in meeting its own public API/contract?

[0] It's hard to make that analogy with Postgres b/c it only has one storage engine, but of course the separation still exists.