In a traditional database such as Postgres, queries are routed through a database server that handles both queries and updates, and is quite close to the storage. Reading excess data while executing a query is less of an issue as only the relevant data is eventually streamed to the client.

Datomic is quite different, in that peers (the other services that query Datomic data) execute the query engine library, and directly read the raw data from the store (or from a cache, as Datomic data is immutable). This design makes it easy to scale reads, but introduces the locality issues that the partitioning enhancement addresses.

It’s quite apples and oranges.