Message-ID: <85eaf260a4be2e08376145a9d6a69d9d74e89daa.camel@j-davis.com>
Subject: Re: Statistics Import and Export
From: Jeff Davis <pgsql@j-davis.com>
To: Corey Huinker <corey.huinker@gmail.com>
Cc: Matthias van de Meent <boekewurm+postgres@gmail.com>, Bruce Momjian
 <bruce@momjian.us>, Tom Lane <tgl@sss.pgh.pa.us>, Nathan Bossart
 <nathandbossart@gmail.com>, 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>,  Tomas Vondra
 <tomas.vondra@enterprisedb.com>, alvherre@alvh.no-ip.org
Date: Mon, 22 Jul 2024 17:45:50 -0700
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On Mon, 2024-07-22 at 12:05 -0400, Corey Huinker wrote:
> Attached is v24, incorporating Jeff's feedback - looping an arg data
> structure rather than individually checking each param type being the
> biggest of them.
>=20

Thank you for splitting up the patches more finely.

v24-0001:

  * pg_set_relation_stats(): the warning: "cannot export statistics
prior to version 9.2" doesn't make sense because the function is for
importing. Reword.

  * I really think there should be a transactional option, just another
boolean, and if it has a default it should be true. This clearly has
use cases for testing plans, etc., and often transactions will be the
right thing there. This should be a trivial code change, and it will
also be easier to document.

  * The return type is documented as 'void'? Please change to bool and
be clear about what true/false returns really mean. I think false means
"no updates happened at all, and a WARNING was printed indicating why"
whereas true means "all updates were applied successfully".

  * An alternative would be to have an 'error_ok' parameter to say
whether to issue WARNINGs or ERRORs. I think we already discussed that
and agreed on the boolean return, but I just want to confirm that this
was a conscious choice?

  * tests should be called stats_import.sql; there's no exporting going
on

  * Aside from the above comments and some other cleanup, I think this
is a simple patch and independently useful. I am looking to commit this
one soon.

v24-0002:

  * Documented return type is 'void'

  * I'm not totally sure what should be returned in the event that some
updates were applied and some not. I'm inclined to say that true should
mean that all updates were applied -- otherwise it's hard to
automatically detect some kind of typo.

  * Can you describe your approach to error checking? What kinds of
errors are worth checking, and which should we just put into the
catalog and let the planner deal with?

  * I'd check stakindidx at the time that it's incremented rather than
summing boolean values cast to integers.

v24-0003:

  * I'm not convinced that we should continue when a stat name is not
text. The argument for being lenient is that statistics may change over
time, and we might have to ignore something that can't be imported from
an old version into a new version because it's either gone or the
meaning has changed too much. But that argument doesn't apply to a
bogus call, where the name/value pairs get misaligned or something.

Regards,
	Jeff Davis