Re: Fix BUG #17335: Duplicate result rows in Gather node

From: Yura Sokolov <y(dot)sokolov(at)postgrespro(dot)ru>
To: David Rowley <dgrowleyml(at)gmail(dot)com>
Cc: PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Fix BUG #17335: Duplicate result rows in Gather node
Date: 2022-01-17 07:49:05
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В Сб, 01/01/2022 в 15:19 +1300, David Rowley пишет:
> On Fri, 31 Dec 2021 at 00:14, Yura Sokolov <y(dot)sokolov(at)postgrespro(dot)ru> wrote:
> > Problem:
> > - Append path is created with explicitely parallel_aware = true
> > - It has two child, one is trivial, other is parallel_aware = false .
> > Trivial child is dropped.
> > - Gather/GatherMerge path takes Append path as a child and thinks
> > its child is parallel_aware = true.
> > - But Append path is removed at the last since it has only one child.
> > - Now Gather/GatherMerge thinks its child is parallel_aware, but it
> > is not.
> > Gather/GatherMerge runs its child twice: in a worker and in a leader,
> > and gathers same rows twice.
> Thanks for the report. I can confirm that I can recreate the problem
> with your script.
> I will look into this further later next week.

Good day, David.

Excuse me for disturbing.
Any update on this?
Any chance to be fixed in next minor release?
Could this simple fix be merged before further improvements?


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