Also this architectures assume there's no need to do the dreaded "network locking", which for some problems regarding dispatch and avoiding triggering expensive/non idempotent batch jobs on background needs to be done. If you want to rely on SQL to do all the locking for you this usually doesn't scale.
> If you want to rely on SQL to do all the locking for you this usually doesn't scale.
I suspect you have a mis-adjusted notion of "usually". "Usually", as in, for the majority of systems designed and in-use in the world, a well tuned, reliable RDBMS will be able to do this absolutely fine. The scale of systems that the world needs vs the quantity of them is an extremely long tailed curve.
