On 3 March 2016 at 22:57, David Rowley <david.row...@2ndquadrant.com> wrote: > On 3 March 2016 at 18:04, Tom Lane <t...@sss.pgh.pa.us> wrote: >> If you come across any points where it seems like it could be >> done better or more easily, that would be tremendously valuable feedback >> at this stage. > > Well since you mention it, I started on hash grouping and it was > rather simple and clean as in create_agg_path() I just created a chain > of the required paths and let create_plan() recursively build the > Finalize Aggregate -> Gather -> Partial Aggregate -> Seq Scan plan. > That was rather simple, and actually very nice when compared to how > things are handled in today's grouping planner. When it comes to Group > Aggregate I notice that you're using a RollupPath rather than an > AggPath even when there's no grouping sets. This also means that > create_agg_path() is only ever used for the AGG_HASHED strategy, even > though the 'strategy' is passed as a parameter to that function, so it > seemed prudent to me, to make sure all strategies are handled properly > there. > > My gripe is that I've added the required code to build the parallel > group aggregate to create_agg_path() already, but since Group > Aggregate uses the RollupPath I'm forced to add code in > create_rollup_plan() which manually stacks up Plan nodes rather than > just dealing with Paths and create_plan() and its recursive call > magic. > > I can't quite see any blocker for not doing this, so would you object > to separating out the treatment of Group Aggregate and Grouping Sets > in create_grouping_paths() ? I think it would require less code > overall.
Actually I might have jumped the gun a little here with my complaint. I think it does not matter about this as I've just coded Parallel Group Aggregate part to reuse create_agg_path(), but left the non-parallel version to make use of create_rollup_path(). I don't think I want to go to the trouble of parallel grouping sets at this stage anyway. -- David Rowley http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
