Author here -- it is "free" in the sense that all the effort we put into DataFusion flows directly into IOx. But we do put a lot of effort into DataFusion
I didn't mean to imply it's free as in no effort goes into. Just that the underlying library provides it so it's less effort on top of the already significant effort going into DataFusion itself.
Ah -- got it! This is the beauty of aligning ourselves with technologies like Arrow, Parquet and DataFusion. We can share as well as benefit from the efforts of the broader community