Date: Sun, 12 Dec 2021 15:32:10 -0600
From: Justin Pryzby <pryzby@telsasoft.com>
To: Tomas Vondra <tomas.vondra@enterprisedb.com>
Cc: Zhihong Yu <zyu@yugabyte.com>,
	Jaime Casanova <jcasanov@systemguards.com.ec>,
	pgsql-hackers@postgresql.org
Subject: Re: extended stats on partitioned tables
Message-ID: <20211212213210.GP17618@telsasoft.com>
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On Sun, Dec 12, 2021 at 05:17:10AM +0100, Tomas Vondra wrote:
> The one thing bugging me a bit is that the regression test checks only a
> GROUP BY query. It'd be nice to add queries testing MCV/dependencies
> too, but that seems tricky because most queries will use per-partitions
> stats.

You mean because the quals are pushed down to the scan node.

Does that indicate a deficiency ?

If extended stats are collected for a parent table, selectivity estimates based
from the parent would be better; but instead we use uncorrected column
estimates from the child tables.