Message-ID: <bd72b9c9ce285350c5ce247f43b21bea39f24326.camel@j-davis.com>
Subject: Re: Statistics Import and Export
From: Jeff Davis <pgsql@j-davis.com>
To: Corey Huinker <corey.huinker@gmail.com>, jian he
	 <jian.universality@gmail.com>
Cc: Nathan Bossart <nathandbossart@gmail.com>, Bruce Momjian
 <bruce@momjian.us>,  Matthias van de Meent <boekewurm+postgres@gmail.com>,
 Tom Lane <tgl@sss.pgh.pa.us>, Magnus Hagander <magnus@hagander.net>, 
 Stephen Frost <sfrost@snowman.net>, Ashutosh Bapat
 <ashutosh.bapat.oss@gmail.com>, Peter Smith <smithpb2250@gmail.com>,
 PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, 
 alvherre@alvh.no-ip.org
Date: Mon, 20 Jan 2025 11:11:54 -0800
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On Mon, 2025-01-20 at 10:58 -0500, Corey Huinker wrote:
> That is where all statistics were previously. Others felt very
> strongly that they should be mixed in to SECTION_DATA and
> SECTION_POST_DATA.

I believe you are referring to Tom's statement that "it'll be a
serious, serious error for [stats] not to be SECTION_DATA". The
statement is somewhat softened by the sentence that follows, and
slightly more by [2]. But it's pretty clear that SECTION_POST_DATA is,
at best, an implementation comprosmise.

The reason we need to put some stats in SECTION_POST_DATA is because of
the hack to resolve MVs that depend on primary keys by moving the MV
into SECTION_POST_DATA. (An MV can depend on a primary key when the
query has a GROUP BY that relies on functional dependencies to be
valid.) That's a fairly marginal case, and one we might be able to
resolve a better way in the future, so I don't think that should drive
the design.

Reagrding [2] and [3], we might need to reconsider the behavior of the
--data-only option. I asked for the v38 behavior out of a sense of
consistency and completeness (the ability to express whatever
combination of things the user might want). But re-reading those
messages, we might want --data-only to include the stats?

Regards,
	Jeff Davis

[1]
https://www.postgresql.org/message-id/1798867.1712376328@sss.pgh.pa.us
[2]
https://www.postgresql.org/message-id/3156140.1713817153%40sss.pgh.pa.us
[3]
https://www.postgresql.org/message-id/3228677.1713844341%40sss.pgh.pa.us