Re: Add proper planner support for ORDER BY / DISTINCT aggregates

On Fri, 16 Dec 2022 at 00:10, David Rowley <dgrowleyml@gmail.com> wrote:
> v3-0002 removes the 1.5 x cost pessimism from incremental sort and
> also rewrites how we make incremental sort paths.  I've now gone
> through the remaining places where we create an incremental sort path
> to give all those the same treatment that I'd added to
> add_paths_to_grouping_rel(). There was a 1 or 2 plan changes in the
> regression tests.  One was the isolation test change, which I claim to
> be a broken test and should be fixed another way.  The other was
> performing a Sort on the cheapest input path which had presorted keys.
> That plan now uses an Incremental Sort to make use of the presorted
> keys. I'm happy to see just how much redundant code this removes.
> About 200 lines.

I've now pushed this patch. Thanks for the report and everyone for all
the useful discussion. Also Richard for the review.

> v3-0003 adds the enable_presorted_aggregate GUC.

This I've moved off to [1]. We tend to have lengthy discussions about
GUCs, what to name them and if we actually need them. I didn't want to
bury that discussion in this old and already long thread.

David

[1] https://postgr.es/m/CAApHDvqzuHerD8zN1Qu=d66e3bp1=9iFn09ZiQ3Zug_Phi6yLQ@mail.gmail.com