Re: Gather Merge

On Thu, Mar 9, 2017 at 8:21 AM, Rushabh Lathia <rushabh(dot)lathia(at)gmail(dot)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

So evidently there is at least one more bug here.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
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