If each client has its own database, does that mean you're automating the infra to turn on a new instance for each database, and then routing requests appropriately? Not too hard with k8, I suppose. Or if you add new clients infrequently enough it's a manual task. But you wouldn't do this for each user - it assumes you have some higher level of organization (client/tenant/org/etc).

Sounds like these are different ways of manually sharding the database?