Date: Mon, 9 Aug 2021 16:02:33 -0400
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Andres Freund <andres@anarazel.de>
Cc: Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>,
	yuzuko <yuzukohosoya@gmail.com>,
	Tomas Vondra <tomas.vondra@enterprisedb.com>,
	David Steele <david@pgmasters.net>,
	Kyotaro Horiguchi <horikyota.ntt@gmail.com>,
	Justin Pryzby <pryzby@telsasoft.com>,
	Daniel Gustafsson <daniel@yesql.se>,
	Amit Langote <amitlangote09@gmail.com>,
	Masahiko Sawada <masahiko.sawada@2ndquadrant.com>,
	Laurenz Albe <laurenz.albe@cybertec.at>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
	Greg Stark <stark@mit.edu>
Subject: Re: Autovacuum on partitioned table (autoanalyze)
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Hi

On 2021-Jul-27, Andres Freund wrote:

> Isn't this going to create a *lot* of redundant sampling?  Especially if you
> have any sort of nested partition tree. In the most absurd case a partition
> with n parents will get sampled n times, solely due to changes to itself.

It seems to me that you're barking up the wrong tree on this point.
This problem you describe is not something that was caused by this
patch; ANALYZE has always worked like this.  We have discussed the idea
of avoiding redundant sampling, but it's clear that it is not a simple
problem, and solving it was not in scope for this patch.

> Additionally, while analyzing all child partitions for a partitioned tables
> are AccessShareLock'ed at once. If a partition hierarchy has more than one
> level, it actually is likely that multiple autovacuum workers will end up
> processing the ancestors separately.  This seems like it might contribute to
> lock exhaustion issues with larger partition hierarchies?

I agree this seems a legitimate problem.

-- 
Álvaro Herrera              Valdivia, Chile  —  https://www.EnterpriseDB.com/