On Sun, Jul 7, 2019 at 8:34 AM Tomas Vondra <tomas.von...@2ndquadrant.com> wrote: > > On Thu, Jul 04, 2019 at 09:29:49AM -0400, James Coleman wrote: > >On Tue, Jun 25, 2019 at 7:22 PM Tomas Vondra > ><tomas.von...@2ndquadrant.com> wrote: > >> > >> On Tue, Jun 25, 2019 at 04:53:40PM -0400, James Coleman wrote: > >> > > >> >Unrelated: if you or someone else you know that's more familiar with > >> >the parallel code, I'd be interested in their looking at the patch at > >> >some point, because I have a suspicion it might not be operating in > >... > >> So I've looked into that, and the reason seems fairly simple - when > >> generating the Gather Merge paths, we only look at paths that are in > >> partial_pathlist. See generate_gather_paths(). > >> > >> And we only have sequential + index paths in partial_pathlist, not > >> incremental sort paths. > >> > >> IMHO we can do two things: > >> > >> 1) modify generate_gather_paths to also consider incremental sort for > >> each sorted path, similarly to what create_ordered_paths does > >> > >> 2) modify build_index_paths to also generate an incremental sort path > >> for each index path > >> > >> IMHO (1) is the right choice here, because it automatically does the > >> trick for all other types of ordered paths, not just index scans. So, > >> something like the attached patch, which gives me plans like this: > >... > >> But I'm not going to claim those are total fixes, it's the minimum I > >> needed to do to make this particular type of plan work. > > > >Thanks for looking into this! > > > >I intended to apply this to my most recent version of the patch (just > >sent a few minutes ago), but when I apply it I noticed that the > >partition_aggregate regression tests have several of these failures: > > > >ERROR: could not find pathkey item to sort > > > >I haven't had time to look into the cause yet, so I decided to wait > >until the next patch revision. > > > > I wanted to investigate this today, but I can't reprodure it. How are > you building and running the regression tests? > > Attached is a patch adding the incremental sort below gather merge, and > also tweaking the costing. But that's mostly for and better planning > decisions, I don't get any pathkey errors even with the first patch.
On 12be7f7f997debe4e05e84b69c03ecf7051b1d79 (the last patch I sent, which is based on top of 5683b34956b4e8da9dccadc2e3a53b86104ebb33), I did this: patch -p1 < ~/Downloads/parallel-incremental-sort.patch <rebuild> (FWIW I configure with ./configure --prefix=$HOME/postgresql-test --enable-cassert --enable-debug --enable-depend CFLAGS="-ggdb -Og -g3 -fno-omit-frame-pointer -DOPTIMIZER_DEBUG") make check-world And I get the attached regression failures. James Coleman
regression.diffs
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regression.out
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