Question about SubsetTransformer

[Renjie Liu <li...@gmail.com>]

Hi, drill devs:
I'm developing a storage plugin for our own storage engine and I'm
confusing about the SubsetTransformer  class while reading the source code.
It seems that its goal is to find all physical implementations of an input
and add it directly to the current as input. But I think this maybe
unnecessary since volcano planner will search rules and do the
transformation for us. What I guess is that this can accelerate the
optimization process.
-- 
Liu, Renjie
Software Engineer, MVAD