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In-Reply-To: <20190614032439.vrv7tvvyez5j2xog@momjian.us>
From: David Rowley <david.rowley@2ndquadrant.com>
Date: Fri, 14 Jun 2019 15:57:45 +1200
Message-ID: 
 <CAKJS1f-DGABDX3QHCGsi6UmDsxdmFkiKUYWQLs8pzeWLnOgnRw@mail.gmail.com>
Subject: Re: PostgreSQL 12: Feature Highlights
To: Bruce Momjian <bruce@momjian.us>
Cc: Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>,
	"Jonathan S. Katz" <jkatz@postgresql.org>,
 pgsql-advocacy@lists.postgresql.org
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On Fri, 14 Jun 2019 at 15:24, Bruce Momjian <bruce@momjian.us> wrote:
>
> On Wed, May 22, 2019 at 12:33:10PM +1200, David Rowley wrote:
> > On Wed, 22 May 2019 at 02:55, Bruce Momjian <bruce@momjian.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.

That looks fine. Thank you.

-- 
 David Rowley                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services