Re: [HACKERS] Gather Merge - Mailing list pgsql-hackers

On Thu, Mar 9, 2017 at 8:21 AM, Rushabh Lathia <rushabh.lathia@gmail.com> wrote:
> Thanks Robert for committing this.
>
> My colleague Neha Sharma found one regression with the patch. I was about
> to send this mail and noticed that you committed the patch.

Oops.  Bad timing.

> postgres=# explain select aid from pgbench_accounts where aid % 25= 0 group
> by aid;
> ERROR:  ORDER/GROUP BY expression not found in targetlist

I think your fix for this looks right, although I would write it this way:

-    gm_plan->plan.targetlist = subplan->targetlist;
+    gm_plan->plan.targetlist = build_path_tlist(root, &best_path->path);

The second part of your fix looks wrong.  I think you want this:

                         create_gather_merge_path(root,
                                                  grouped_rel,
                                                  subpath,
-                                                 NULL,
+                                                 partial_grouping_target,
                                                  root->group_pathkeys,
                                                  NULL,
                                                  &total_groups);

That will match the create_gather_path case.

This test case is still failing for me even with those fixes:

rhaas=# select aid+1 from pgbench_accounts group by aid+1;
ERROR:  could not find pathkey item to sort