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. James Coleman
