[flowerlad]

> You need to have some sort of duplication unless you want big bottlenecks, performance penalties

I think that's called a cache. You can still have solid database design at the core. Then add redis on top of it.

[Raidion]

It can be non cached data as well. Imagine a data that needs to be sorted by data that's owned by another another service. You need to replicate the data as you can't do a join+sort between the data coming from two apis effectively. You don't treat that data as a source of truth, but do use it some UI purposes.