Re: PostgreSQL 12: Feature Highlights

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>
Cc: Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>, "Jonathan S(dot) Katz" <jkatz(at)postgresql(dot)org>, pgsql-advocacy(at)lists(dot)postgresql(dot)org
Subject: Re: PostgreSQL 12: Feature Highlights
Date: 2019-06-14 03:24:39
Message-ID: 20190614032439.vrv7tvvyez5j2xog@momjian.us
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On Wed, May 22, 2019 at 12:33:10PM +1200, David Rowley wrote:
> On Wed, 22 May 2019 at 02:55, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> > This brings up a few points. First, it seems the change affects
> > partitioned tables and UNION ALL, which means it probably needs to be
> > listed in two sections. Second, is it only parallelism paths that are
> > added? I am not sure if people care about a node being removed,
> > especially when the might not even know we do that step, but they do
> > care if there are new optimization possibilities.
>
> Like Amit, I think the optimizer section is fine. Another thing that
> is affected is that you may no longer get a Materialize node in the
> plan. Previously you might have gotten something like Merge Join ->
> Materialize -> Append -> Seq Scan, now you might just get Merge Join
> -> Seq Scan. This is because Append / MergeAppend don't support mark
> and restore. Removing them would allow the materialize node to be
> skipped in cases where the single subpath of the Append does support
> mark and restore.

How is this patch for the item? I put it in the Optimizer section.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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