A recommendation came in from a trusted source that QuestDB is worth evaluating.  In their own words:

"QuestDB is a relational column-oriented database designed for time series and event data. It uses SQL with extensions for time series to assist with real-time analytics."

No JDBC so not a drop-in replacement for one of the many databases that support JDBC.  Does have a REST API, so I could imagine cobbling together something that exposes a subset of JDBC with a REST interface to the datastore.

Column store but don't have to work with the joyful, easy-to-understand constructs of k and q - it might catch on...