From: | David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> |
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To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Removing [Merge]Append nodes which contain a single subpath |
Date: | 2017-10-26 11:17:00 |
Message-ID: | CAKJS1f_zbhQ=fFGqZPHXv0Eyga7fpmOzQKd3xsy4UHnhknnU6g@mail.gmail.com |
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Lists: | pgsql-hackers |
On 26 October 2017 at 23:30, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Wed, Oct 25, 2017 at 11:59 PM, David Rowley
> <david(dot)rowley(at)2ndquadrant(dot)com> wrote:
>> As of today, because we include this needless [Merge]Append node, we
>> cannot parallelise scans below the Append.
>
> Without disputing your general notion that singe-child Append or
> MergeAppend nodes are a pointless waste, how does a such a needless
> node prevent parallelizing scans beneath it?
hmm, I think I was wrong about that now. I had been looking over the
regression test diffs after having made tenk1 a partitioned table with
a single partition containing all the rows, but it looks like I read
the diff backwards. The planner actually parallelized the Append
version, not the non-Append version, like I had previously thought.
--
David Rowley http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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