I used to work for a competitor to Denodo. Query optimization for data virtualization/federation across heterogenous systems is very complicated - that much I

I used to work for a competitor to Denodo. Query optimization for data virtualization/federation across heterogenous systems is very complicated - that much I can assure you. You might be interested in Dremio (which is a modernized and open source version of Drill, but also has a commercial version) too. I had previously studied Spark, PrestoDb and Hive, among other things, for similar purposes. If you ever want to chat feel free to contact me via my profile email.