[np422]

If your performance bottleneck is at the database layer it's a difficult problem to solve, scaling relational databases requires all kinds of witchcraft and magic such as read-only replicas, sharding, result-caching ...

But it is very simple to add another application server and update your load-balancers configuration.

Some large (internet) applications have moved operations such as joins to the application and only use the database for simple storage.

I think it's a reasonable advice.