Datomic is just a Prolog logical layer on top of traditional RDBMS (e.g. Postgres, H2, etc).

I'd agree it probably doesn't quite apply to this case, but there are similarities from what I've researched, and I think that description doesn't quite do it justice. First being that datomic is temporal with full on-demand history, which I think is a big deal; and has a serialized writer, n-reader architecture. As to how it may relate to this problem, I believe peer applications (in-process) for on-prem are able to exploit locality with the full indexes in-memory without round-trip queries - also the case for ions with datomic cloud. I'll let anyone more experienced clarify or correct me. The concept at least is really cool; I hope to give it a real test drive some time soon.

No, Datomic storage is unbundled, prod configurations target basically DynamoDB.