unfortunately this got a bit broken by the disk-based hash aggregation, committed today, and so it needs a rebase. I've started looking at the patch before that, and I have it rebased on e00912e11a9e (i.e. the commit before the one that breaks it).
I spent the day to look into the details of the hash spill patch and finally can
successfully rebase it, I tested the first 5 patches and they all passed the
installcheck, the 0006-parallel-xxx.path is not tested yet and I also need to
make hash spill work in the final stage of parallel grouping sets, will do that
tomorrow.
the conflicts mainly located in the handling of hash spill for grouping sets,
the 0004-reorganise-xxxx patch also make the refilling the hash table stage easier and
can avoid the nullcheck in that stage.
Attached is the rebased patch series (now broken), with a couple of commits with some minor cosmetic changes I propose to make (easier than explaining it on a list, it's mostly about whitespace, comments etc). Feel free to reject the changes, it's up to you.
Thanks, I will enhance the comments and take care of the whitespace.
I'll continue doing the review, but it'd be good to have a fully rebased version.