Re: [HACKERS] Removing [Merge]Append nodes which contain a single subpath

From: David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>
To: Michael Paquier <michael(dot)paquier(at)gmail(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [HACKERS] Removing [Merge]Append nodes which contain a single subpath
Date: 2017-12-06 23:41:50
Message-ID: CAKJS1f8n09ELtR3FC4JfcX20V-jT2NVw7huZuE-0UyyUEaY2Sw@mail.gmail.com
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On 30 November 2017 at 16:04, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> wrote:
> I've attached a patch which fixes the conflict with the regression test
> expected output in inherits.out. I've also made changes to the expected
> output in the new partition_prune test's expected output.

I've attached an updated patch which fixes the conflicts caused by ab727167.

Also, I've attached a patch which is not intended for commit which
shows the subtle differences between directly querying a partitioned
table with a single remaining leaf partition to scan vs directly
querying the leaf partition itself. The regression test failures seen
with both patches applied highlight the differences.

While rebasing this today I also noticed that we won't properly detect
unique joins in add_paths_to_joinrel() as we're still testing for
uniqueness against the partitioned parent rather than the only child.
This is likely not a huge problem since we'll always get a false
negative and never a false positive, but it is a missing optimisation.
I've not thought of how to solve it yet, it's perhaps not worth going
to too much trouble over.

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

Attachment Content-Type Size
remove_singleton_appends_2017-12-07.patch application/octet-stream 59.5 KB
remove_singleton_appends_examples_of_differences_2017-12-07.patch application/octet-stream 108.5 KB

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