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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Jeff Davis <pgsql@j-davis.com>
Cc: Corey Huinker <corey.huinker@gmail.com>
Cc: Stephen Frost <sfrost@snowman.net>
Cc: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Cc: Matthias van de Meent <boekewurm+postgres@gmail.com>
Cc: Peter Smith <smithpb2250@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Cc: Tomas Vondra <tomas.vondra@enterprisedb.com>
Subject: Re: Statistics Import and Export
Date: Mon, 01 Apr 2024 13:18:46 -0400
Message-ID: <1097772.1711991926@sss.pgh.pa.us> (raw)
In-Reply-To: <57e2d0c87d30e9b0dfb80f5b5d6a1a82a2539f10.camel@j-davis.com>
References: <Zei1xMGH8SJS9yoc@tamriel.snowman.net>
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	<57e2d0c87d30e9b0dfb80f5b5d6a1a82a2539f10.camel@j-davis.com>

Jeff Davis <pgsql@j-davis.com> writes:
> On Sat, 2024-03-30 at 20:08 -0400, Tom Lane wrote:
>> I haven't looked at the details, but I'm really a bit surprised
>> by Jeff's assertion that CREATE INDEX destroys statistics on the
>> base table.  That seems wrong from here, and maybe something we
>> could have it not do.  (I do realize that it recalculates reltuples
>> and relpages, but so what?  If it updates those, the results should
>> be perfectly accurate.)

> In the v15 of the patch I was looking at, "pg_dump -s" included the
> statistics. The stats appeared first in the dump, followed by the
> CREATE INDEX commands. The latter overwrote the relpages/reltuples set
> by the former.

> While zeros are the right answers for a schema-only dump, it defeated
> the purpose of including relpages/reltuples stats in the dump, and
> caused the pg_upgrade TAP test to fail.

> You're right that there are a number of ways this could be resolved --
> I don't think it's an inherent problem.

I'm inclined to call it not a problem at all.  While I do agree there
are use-cases for injecting false statistics with these functions,
I do not think that pg_dump has to cater to such use-cases.

In any case, I remain of the opinion that stats are data and should
not be included in a -s dump (with some sort of exception for
pg_upgrade).  If the data has been loaded, then a subsequent
overwrite by CREATE INDEX should not be a problem.

			regards, tom lane





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