> KQuery does not yet implement the join operator.
Whilst I applaud this book writing initiative, completing it could easily become a lifetime's work! It will be a fascinating journey to follow along with in any case.
Apache Arrow could (and hopefully will) really shake up the database industry in the years ahead. Whatever eventually supplants Postgres is quite likely going to be based on Arrow - polyglot zero-copy vector processing is the future.
Aside: for anyone looking for a more theoretical overview of databases and query languages, this ~free Foundations of Databases book still holds up well http://webdam.inria.fr/Alice/
Idk, but I'd rather see a new iteration of PostgreSQL, similiar to Hydra[0], with a new engine become the upstream instead of a whole new database.
There's a lot of experience about db operation and how to approach MVCC encoded in PostgreSQL that shouldn't be underestimated.