In-memory data stores still typically have a concept of "durability" which you can think of as "the same transaction is committed on all servers in {some defini

In-memory data stores still typically have a concept of "durability" which you can think of as "the same transaction is committed on all servers in {some definition of a replica group}." So like any disk backed store, all servers see transactions consistently, and all have a copy of the data. Obviously, there's no replication/transaction processing occurring when you're just storing stuff in an ordinary hashmap. Hence the Fake* naming.