Ask HN: What is the current state of art in distributed databases/datastores?

I had gone through a survey course while in grad school a few years ago. Riak, HBase, CouchDB were the shiny new things. I kinda lost track of things after school, but want to check back in again on what is the latest.

What is the current state of art? Is there a book that I can read up on this or better yet, some academic course/offering that covers this? Mostly looking for what design decisions/algorithms/data structures used by the databases. Is the Klepmann book (DDIA) slightly out of date now or still very much relevant?

Thank you!!