Date: Tue, 17 Jan 2023 15:00:50 -0600
From: Justin Pryzby <pryzby@telsasoft.com>
To: Bruce Momjian <bruce@momjian.us>
Cc: Nathan Bossart <nathandbossart@gmail.com>,
	Laurenz Albe <laurenz.albe@cybertec.at>,
	Tomas Vondra <tomas.vondra@enterprisedb.com>,
	Robert Haas <robertmhaas@gmail.com>,
	=?iso-8859-1?Q?=C1lvaro?= Herrera <alvherre@alvh.no-ip.org>,
	yuzuko <yuzukohosoya@gmail.com>, pgsql-hackers@postgresql.org
Subject: Re: document the need to analyze partitioned tables
Message-ID: <20230117210050.GX9837@telsasoft.com>
References: <20211008125822.GJ27491@telsasoft.com>
 <681e76ad-3a7b-ea3c-b6b0-55946239c49b@enterprisedb.com>
 <20220121180200.GM23027@telsasoft.com>
 <19c248d9-3687-9e0f-0b1a-2adad1de6fbe@enterprisedb.com>
 <CA+TgmoYNaSWQg1W3JZ62UBM9iMphBpVJr_oDxn5T1X_viOPBtw@mail.gmail.com>
 <20220315230011.GZ28503@telsasoft.com>
 <88903179-5ce2-3d4d-af43-7830372bdcb6@enterprisedb.com>
 <1fd81ddc7710a154834030133c6fea41e55c8efb.camel@cybertec.at>
 <20230112232747.GA2111950@nathanxps13>
 <Y8cKxCRXBwEVFfot@momjian.us>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <Y8cKxCRXBwEVFfot@momjian.us>
User-Agent: Mutt/1.9.4 (2018-02-28)
Archived-At: 
 <https://www.postgresql.org/message-id/20230117210050.GX9837%40telsasoft.com>
Precedence: bulk

On Tue, Jan 17, 2023 at 03:53:24PM -0500, Bruce Momjian wrote:
> On Thu, Jan 12, 2023 at 03:27:47PM -0800, Nathan Bossart wrote:
> > On Wed, Oct 05, 2022 at 10:37:01AM +0200, Laurenz Albe wrote:
> > > On Mon, 2022-03-28 at 15:05 +0200, Tomas Vondra wrote:
> > >> I've pushed the last version, and backpatched it to 10 (not sure I'd
> > >> call it a bugfix, but I certainly agree with Justin it's worth
> > >> mentioning in the docs, even on older branches).
> > > 
> > > I'd like to suggest an improvement to this.  The current wording could
> > > be read to mean that dead tuples won't get cleaned up in partitioned tables.
> > 
> > Well, dead tuples won't get cleaned up in partitioned tables, as
> > partitioned tables do not have storage.  But I see what you mean.  Readers
> > might misinterpret this to mean that autovacuum will not process the
> > partitions.  There's a good definition of what the docs mean by
> > "partitioned table" [0], but FWIW it took me some time before I
> > consistently read "partitioned table" to mean "only the thing with relkind
> > set to 'p'" and not "both the partitioned table and its partitions."  So,
> > while the current wording it technically correct, I think it'd be
> > reasonable to expand it to help avoid confusion.
> > 
> > Here is my take on the wording:
> > 
> > 	Since all the data for a partitioned table is stored in its partitions,
> > 	autovacuum does not process partitioned tables.  Instead, autovacuum
> > 	processes the individual partitions that are regular tables.  This
> > 	means that autovacuum only gathers statistics for the regular tables
> > 	that serve as partitions and not for the partitioned tables.  Since
> > 	queries may rely on a partitioned table's statistics, you should
> > 	collect statistics via the ANALYZE command when it is first populated,
> > 	and again whenever the distribution of data in its partitions changes
> > 	significantly.
> 
> Uh, what about autovacuum's handling of partitioned tables?  This makes
> it sound like it ignores them because it talks about manual ANALYZE.

If we're referring to the *partitioned* table, then it does ignore them.
See:

|commit 6f8127b7390119c21479f5ce495b7d2168930e82
|Author: Alvaro Herrera <alvherre@alvh.no-ip.org>
|Date:   Mon Aug 16 17:27:52 2021 -0400
|
|    Revert analyze support for partitioned tables

Maybe (all?) the clarification the docs need is to say:
"Partitioned tables are not *themselves* processed by autovacuum."

-- 
Justin