Re: [HACKERS] Partition-wise aggregation/grouping

On Thu, Feb 8, 2018 at 8:05 AM, Jeevan Chalke
<jeevan(dot)chalke(at)enterprisedb(dot)com> wrote:
> In this attached version, I have rebased my changes over new design of
> partially_grouped_rel. The preparatory changes of adding
> partially_grouped_rel are in 0001.

I spent today hacking in 0001; results attached. The big change from
your version is that this now uses generate_gather_paths() to add
Gather/Gather Merge nodes (except in the case where we sort by group
pathkeys and then Gather Merge) rather than keeping all of the bespoke
code. That turned up to be a bit less elegant than I would have liked
-- I had to an override_rows argument to generate_gather_paths to make
it work. But overall I think this is still a big improvement, since
it lets us share code instead of duplicating it. Also, it potentially
lets us add partially-aggregated but non-parallel paths into
partially_grouped_rel->pathlist and that should Just Work; they will
get the Finalize Aggregate step but not the Gather. With your
arrangement that wouldn't work.

Please review/test.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company