Ah gotcha.

Isn't that a hard barrier/limit to scale then (as well as support)? Would it even be possible to run say a 5 million user Lemmy instance with a single write postgres DB (I assume compute can be load balanced, you can utilize CDNs for media content, can heavily cache the API, and that it supports read replicas?)

Nevermind 10, 30, or 50 million user communities 🤔

Though at that point you're essentially just lighting your bank account on fire for infra costs.