So, I did an easy migration of an analytics app from elasticsearch to ClickHouse: what made it easy was (a) we could replay an event stream to regenerate the database and (b) we had interfaces around the database defined in terms of the questions we needed the database to answer, and not in terms of ES-specific concepts.

But, what makes this sort of design so nice is that you can use DB-specific stuff behind the interface because you’re not trying to write all your queries in the minimally supported subset of SQL or something.