Hi folks, I created a design doc https://docs.google.com/document/d/1wo5byn_6K_YOKiPdXNav1zgzt9IBC3SbPvpPnIShtXk/edit?usp=sharing for supporting charset in calcite, per previous discussions on this topic.
One thing I'm not sure is runtime (Codegen on Enumerable and RelExecutor etc) change. Since I/O is decoupled by pluggable points like Schemas#enumerable, that part looks good to me already. I'm sure there are a lot misunderstandings and missing pieces in that doc above, please feel free to leave comments.
