Message-ID: <0b4c098ae3968aa23d6accb691f47bdba143aedd.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, MichaelPaquier <michael@paquier.xyz>
Date: Wed, 05 Feb 2025 20:45:06 -0800
In-Reply-To: <CADkLM=cnYxaNFbAQRMLeOOga0j5pY_V6Tfcn+vjm_rXL=WOF7Q@mail.gmail.com>
References: 
	<CADkLM=cxNaU3O40Y5zGARJBWm-uAvb2hvgZxd=tOu-zTsrHpkQ@mail.gmail.com>
	 <5d3a24216d15ce8a50d0fc085a13a410202014ca.camel@j-davis.com>
	 <CADkLM=fcAneLoFrd41zdxm_1mMZz+wTp5gLJ=Av5JtBi5cBnDQ@mail.gmail.com>
	 <c2bc08dfec336c03f7a7165d1347e2b52cf98b17.camel@j-davis.com>
	 <CADkLM=fyJ-Y-DNk1aW09btZYdXDXS79xT8oFPTQ6sspWHaqdog@mail.gmail.com>
	 <3bd40d2c686608196b8e04c2aaac9c57c447aae6.camel@j-davis.com>
	 <CADkLM=cWc+Zbjnpew9sg346DdRQJj8OSvZjg4fwvpLH10EViJQ@mail.gmail.com>
	 <Z22mcdRo_jTcA7nb@momjian.us>
	 <39770e3aebfdf543fa2215fb300621a54b1b2634.camel@j-davis.com>
	 <Z3MGT8TcCOw4U3H0@momjian.us> <Z3xKtmHxPpHNyqfH@nathan>
	 <CADkLM=c6NHdXU+d+m1yASZ4NT_qye1LCnaU2Vgf8YJ80jJT-Qg@mail.gmail.com>
	 <d8df5339cab25b5720667beaaed8a8bb8e11578c.camel@j-davis.com>
	 <CADkLM=fe4f=YVGHbOGiXV+W2SoJZtcNw1Ta8gYh5UUhxndaVgw@mail.gmail.com>
	 <CACJufxGuRPfd70NwogkRE26cZcKGrR9gjG4OiH18tu=BnyezHA@mail.gmail.com>
	 <CADkLM=fMuVwcxr2aocz4H=LVf2PZsvTNenqEod2PoY1OyCU+kw@mail.gmail.com>
	 <bd72b9c9ce285350c5ce247f43b21bea39f24326.camel@j-davis.com>
	 <CADkLM=cQi+sYpLY6BqybZ8ZWffSU4+1-aEQsShSGbrh3M=Dtcg@mail.gmail.com>
	 <b40b81d38c3a87fdef61e4f7abfbc7f27c7fbcd9.camel@j-davis.com>
	 <CACJufxG6K4EAUROhdr0wkzMh5QyFLmdLZeAoh7Vh0-VbuAtHcw@mail.gmail.com>
	 <CADkLM=fihosVw7fJak6Jq1AdCX8fuZ+7s1_-+AUZR=sdD13zAQ@mail.gmail.com>
	 <CADkLM=cnYxaNFbAQRMLeOOga0j5pY_V6Tfcn+vjm_rXL=WOF7Q@mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
User-Agent: Evolution 3.44.4-0ubuntu2 
MIME-Version: 1.0
Archived-At: <https://www.postgresql.org/message-id/0b4c098ae3968aa23d6accb691f47bdba143aedd.camel%40j-davis.com>
Precedence: bulk

On Wed, 2025-02-05 at 23:01 -0500, Corey Huinker wrote:
> And here's an update to the pg_dump code itself. This currently has
> failing TAP tests for statistics in the custom and dir formats, but
> is working otherwise.

This thread got slightly mixed up, so I'm replying to the v45-0001
posted here, and also in response to Michael's and Corey's comments
from:

https://www.postgresql.org/message-id/Z5H0iRaJc1wnDVLE%40paquier.xyz

On Thu, 2025-01-23 at 16:49 +0900, Michael Paquier wrote:
> On Tue, Jan 21, 2025 at 10:21:51PM -0500, Corey Huinker wrote:
> > After some research, I think that we should treat partitioned
> > indexes like
> > we were before, and just handle the existing special case for
> > regular
> > indexes.
>
> Hmm, why?  Sounds strange to me to not have the same locking
> semantics
> for the partitioned parts, and this even if partitioned indexes don't
> have stats that can be manipulated in relation_stats.c as far as I
> can see.  These stats APIs are designed to be permissive as Jeff
> says.
> Having a better locking from the start makes the whole picture more
> consistent, while opening the door for actually setting real stat
> numbers for partitioned indexes (if some make sense, at some point)?

v45-0001 addresses this by locking both the partitioned index, as well
as its table, in ShareUpdateExclusive mode. That satisfies the in-place
update requirement to take a ShareUpdateExclusiveLock on the
partitioned index, while otherwise being the same as normal indexes
(and therefore unlikely to cause a problem if ANALYZE sets stats on
partitioned indexes in the future).

That means:
  *=C2=A0For indexes: ShareUpdateExclusiveLock on table and AccessShareLock
on index
  * For partitioned indexes: ShareUpdateExclusiveLock on table and
ShareUpdateExclusiveLock on index
  * Otherwise, ShareupdateExclusiveLock on the relation

which makes sense to me. The v45-0001 patch itself could use some
cleanup, but I can take care of that at commit time if we agree on the
locking scheme.

Regards,
	Jeff Davis