I'd like to devise a test query that shows performance gain from this patch, but I'm not sure how to do that. May need help here.
I've been trying for some time but still haven't been able to come up with a test case that shows the performance improvement of this patch. My best guess is that situations that can benefit from direct lookups of SpecialJoinInfo are pretty rare, and the related codes are not in the critical path. So for now I think I'd better withdraw this patch to avoid people wasting time reviewing it.
