From: Tom Lane <tgl@sss.pgh.pa.us>
To: David Rowley <david.rowley@2ndquadrant.com>
cc: Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>,
        Yuzuko Hosoya <hosoya.yuzuko@lab.ntt.co.jp>,
        PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Runtime pruning problem
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Comments: In-reply-to Tom Lane <tgl@sss.pgh.pa.us>
	message dated "Tue, 30 Jul 2019 18:50:32 -0400"
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Date: Tue, 30 Jul 2019 18:56:47 -0400
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I wrote:
> This may be arguing for a change in ruleutils' existing behavior,
> not sure.  But when dealing with traditional-style inheritance,
> I've always thought that Vars above the Append were referring to
> the parent rel in its capacity as the parent, not in its capacity
> as the first child.  With new-style partitioning drawing a clear
> distinction between the parent and all its children, it's easier
> to understand the difference.

OK, so experimenting, I see that it is a change: HEAD does

regression=3D# explain verbose select * from part order by a;
                                   QUERY PLAN                             =
      =

--------------------------------------------------------------------------=
-------
 Sort  (cost=3D362.21..373.51 rows=3D4520 width=3D8)
   Output: part_p1.a, part_p1.b
   Sort Key: part_p1.a
   ->  Append  (cost=3D0.00..87.80 rows=3D4520 width=3D8)
         ->  Seq Scan on public.part_p1  (cost=3D0.00..32.60 rows=3D2260 w=
idth=3D8)
               Output: part_p1.a, part_p1.b
         ->  Seq Scan on public.part_p2_p1  (cost=3D0.00..32.60 rows=3D226=
0 width=3D8)
               Output: part_p2_p1.a, part_p2_p1.b
(8 rows)

The portion of this below the Append is fine, but I argue that
the Vars above the Append should say "part", not "part_p1".
In that way they'd look the same regardless of which partitions
have been pruned or not.

			regards, tom lane