On Tue, 30 Jul 2019 at 02:17, Tomas Vondra <tomas.von...@2ndquadrant.com> wrote:
> On Sun, Jul 21, 2019 at 01:34:22PM +0200, Tomas Vondra wrote: > > > > ... > > > >I wonder if we're approaching this wrong. Maybe we should not reverse > >engineer queries for the various places, but just start with a set of > >queries that we want to optimize, and then identify which places in the > >planner need to be modified. > > > > I've decided to do a couple of experiments, trying to make my mind about > which modified places matter to diffrent queries. But instead of trying > to reverse engineer the queries, I've taken a different approach - I've > compiled a list of queries that I think are sensible and relevant, and > then planned them with incremental sort enabled in different places. > > I don't have any clear conclusions at this point - it does show some of > the places don't change plan for any of the queries, although there may > be some additional query where it'd make a difference. > > But I'm posting this mostly because it might be useful. I've initially > planned to move changes that add incremental sort paths to separate > patches, and then apply/skip different subsets of those patches. But > then I realized there's a better way to do this - I've added a bunch of > GUCs, one for each such place. This allows doing this testing without > having to rebuild repeatedly. > > I'm not going to post the patch(es) with extra GUCs here, because it'd > just confuse the patch tester, but it's available here: > > https://github.com/tvondra/postgres/tree/incremental-sort-20190730 > > There are 10 GUCs, one for each place in planner where incremental sort > paths are constructed. By default all those are set to 'false' so no > incremental sort paths are built. If you do > > SET devel_create_ordered_paths = on; > > it'll start creating the paths in non-parallel in create_ordered_paths. > Then you may enable devel_create_ordered_paths_parallel to also consider > parallel paths, etc. > > The list of queries (synthetic, but hopefully sufficiently realistic) > and a couple of scripts to collect the plans is in this repository: > > https://github.com/tvondra/incremental-sort-tests-2 > > There's also a spreadsheet with a summary of results, with a visual > representation of which GUCs affect which queries. > > Wow, that sounds like an elaborate experiment. But where is this spreadsheet you mentioned ? -- Regards, Rafia Sabih
