> they seriously stored user data in a Postgres database instead of a highly scalable cluster of NoSQL Cassandra instances

Erm …. Not sure I can post on this site knowing my posts are being stored in a SQL database on RDS

lol! Your post is actually stored (canonically) in your own individual SQLite database as of this week! We're in the process of moving our v1 Postgres-based backend to our v2 ScyllaDB-based backend.

You dropped the sqlite idea or is ScyllaDB a joke ?

We'l be using tiny little SQLite databases (one for each user) and (relatively) giant SycllaDB clusters (for aggregation). No joke 😆

OH! Makes more sense. So PDS are individual sqlites and the relay is Syclla, is that right? #nice

Yup, that's right!