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: allow partial union-all and improve parallel subquery costing
Date: 2020-10-13 08:57:23
Message-ID: FRXPR01MB09021F98988B057A636AA4EEB7040@FRXPR01MB0902.DEUPRD01.PROD.OUTLOOK.DE
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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
v1-0001-Allow-partial-UNION-ALL-improve-parallel-subquery.patch text/x-patch 5.0 KB
tpcds-q5-before.txt text/plain 9.7 KB
tpcds-q5-after.txt text/plain 9.1 KB


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