Systems like Erlang/OTP, Akka, Orbit and Orleans/Service Fabric are built on an actor model where domain objects of the system (e.g. Users, Accounts, Invoices, etc.) exist within the cluster and have a an address so they are like having a bunch of mini servers. These servers typically keep their state in memory so they can respond to query messages quickly. Plus the application can unload idle (or no longer necessary) actors and restore their state when they are needed again. It's very similar to the Linked in-memory key-value idea mentioned in the paper.