My big question here is why they decided to move over to MySQL instead of using the Citus (also open source) Postgres extension. They don't mention it, so we don't know whether it was considered, and if so, why it was not selected. Postgres' rapid feature growth in the past years is interesting in itself.
Citus currently has major problems joining non-distributed tables with distributed tables, and it doesn't fully support schemas yet. It's almost there, but not quite.
