Re: allow partial union-all and improve parallel subquery costing

From: Luc Vlaming <luc(at)swarm64(dot)com>
To: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: allow partial union-all and improve parallel subquery costing
Date: 2020-10-14 07:38:08
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It seems I ran the wrong make checks to verify everything is correct (make check instead
of make installcheck-world) and this uncovered another regress test change. I also noticed
the statistics are sometimes giving different row count results so I increased the row
statistics target to make sure the regress output is stable. Updated patch attached which
now successfully runs installcheck-world for v13 and master.

Kind regards,

From: Luc Vlaming <luc(at)swarm64(dot)com>
Sent: Tuesday, October 13, 2020 10:57 AM
To: pgsql-hackers
Subject: allow partial union-all and improve parallel subquery costing


While developing some improvements for TPC-DS queries I found out that with
UNION ALL partial paths are not emitted. Whilst fixing that I also came across
the subquery costing which does not seem to consider parallelism when doing
the costing.

I added a simplified testcase in pg-regress to show this goes wrong, and
attached also a before and after explain output of tpc-ds SF100 query 5
based on version 12.4.

I hope I followed all etiquette and these kind of improvements are welcome.

Kind regards,

Attachment Content-Type Size
v2-0001-Allow-partial-UNION-ALL-improve-parallel-subquery.patch text/x-patch 6.0 KB

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