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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Cc: Corey Huinker <corey.huinker@gmail.com>
Cc: Magnus Hagander <magnus@hagander.net>
Cc: Jeff Davis <pgsql@j-davis.com>
Cc: Stephen Frost <sfrost@snowman.net>
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: Fri, 05 Apr 2024 00:37:32 -0400
Message-ID: <1183619.1712291852@sss.pgh.pa.us> (raw)
In-Reply-To: <CAExHW5sGJhQqBY6THguZd8LAEPGj4jmQyu4rCep+UKyw0mz+cg@mail.gmail.com>
References: <Zei1xMGH8SJS9yoc@tamriel.snowman.net>
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	<790773.1711910899@sss.pgh.pa.us>
	<CADkLM=dracL=rSf+2v+1P4NN_4jq--kyv6Ywh77t4MiiRX98og@mail.gmail.com>
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	<CAExHW5sGJhQqBY6THguZd8LAEPGj4jmQyu4rCep+UKyw0mz+cg@mail.gmail.com>

Ashutosh Bapat <ashutosh.bapat.oss@gmail.com> writes:
> I read that discussion, and it may be ok for pg_upgrade/pg_dump usecase and
> maybe also for IMPORT foreign schema where the SQL is generated by
> PostgreSQL itself. But not for simulating statistics. In that case, if the
> function happily installs statistics cooked by the user and those aren't
> used anywhere, users may be misled by the plans that are generated
> subsequently. Thus negating the very purpose of simulating
> statistics.

I'm not sure what you think the "purpose of simulating statistics" is,
but it seems like you have an extremely narrow-minded view of it.
I think we should allow injecting any stats that won't actively crash
the backend.  Such functionality could be useful for stress-testing
the planner, for example, or even just to see what it would do in
a situation that is not what you have.

Note that I don't think pg_dump or pg_upgrade need to support
injection of counterfactual statistics.  But direct calls of the
stats insertion functions should be able to do so.

			regards, tom lane





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