Feedback-ID: i0fe9450f:Fastmail
Date: Tue, 27 Jan 2026 13:55:06 +0900
From: Michael Paquier <michael@paquier.xyz>
To: Corey Huinker <corey.huinker@gmail.com>
Cc: Chao Li <li.evan.chao@gmail.com>, Tender Wang <tndrwang@gmail.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Extended Statistics set/restore/clear functions.
Message-ID: <aXhFKleXWlooHcy3@paquier.xyz>
References: 
 <CADkLM=dJ4bQ3e4Cc+vaVFmnrL37Y5hPJ1u0AYXE6fSkh_=+sTg@mail.gmail.com>
 <aXAXMwHYF1qyUaP5@paquier.xyz>
 <CADkLM=c3s-BtSebTHggY__DOYFMCdknaLuJHwG0o817o0Q9tNA@mail.gmail.com>
 <aXHGoMAnzV5njUEo@paquier.xyz>
 <CADkLM=c3JivzHNXLt-X_JicYknRYwLTiOCHOPiKagm2_vdrFUg@mail.gmail.com>
 <aXVw4LGO4fWunn4n@paquier.xyz>
 <CADkLM=f4+3_HrXSAaEic5VGGd-fOjS4jGnr1WGJYrL7vf3ZJnw@mail.gmail.com>
 <aXWBhkru03FnrfIW@paquier.xyz>
 <CADkLM=c7DY3Jv6ef0n_MGUJ1FyTMUoT697LbkST05nraVGNHYg@mail.gmail.com>
 <aXca7jnwtzFSYr4s@paquier.xyz>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha512;
	protocol="application/pgp-signature"; boundary="TO71gxnkcQCasJIs"
Content-Disposition: inline
In-Reply-To: <aXca7jnwtzFSYr4s@paquier.xyz>
Archived-At: 
 <https://www.postgresql.org/message-id/aXhFKleXWlooHcy3%40paquier.xyz>
Precedence: bulk


--TO71gxnkcQCasJIs
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline

On Mon, Jan 26, 2026 at 04:42:38PM +0900, Michael Paquier wrote:
> Another side note: I am not sure how the CI or the buldfarm did not
> notice that, but I've found a bug in the tuple initialization logic
> while reviewing more the code, fixed in 114e84c532d1.  Perhaps my
> build environment was more efficient in detecting that.

So, I have done more work on all that, and extracted two more pieces,
applying them:
- The bits for dependencies in the restore function, .
- The pg_dump bits for dependencies and n_distinct, as of
c32fb29e979d.  It was sad here that your posted patch did not use the
keys of statistics_format.h.  A comment was also missing in
AdjustUpgrade.pm, where the code will be able to handle the "version"
tag included in the dumps.

Another thing that I strongly suspect is going to break in the
buildfarm are the cross-version upgrades, because the format of
the pg_dependencies and pg_ndistinct is not completely portable.
While dumping the data for versions older than v18, there are a couple
spaces added due to the way the JSON data is translated.  A similar
issue unfortunately exists for the rounding of the degree numbers in
dependencies.  I am not sure if this is going to break, but if this
breaks I have prepared the following insurance policy for
AdjustUpgrade.pm:
$dump =~ s {\n(\s+'n_distinct',) '.*'::pg_ndistinct}
{\n$1 'EXT_STATS_DATA'::pg_ndistinct}mg;
$dump =~ s {\n(\s+'dependencies',) '.*'::pg_dependencies}
{\n$1 'EXT_STATS_DATA'::pg_dependencies}mg;

This is a filter similar to the "version" field, except that we would
replace all the contents of the pg_ndistinct and pg_dependencies
values inside single quotes, protecting the dump comparisons for the
new and old versions.  Let's see first what the buildfarm says and if
I need to pull this switch.

And it means that at this point we are feature-complete for these two
stats kinds, so there will be at least something for this release even
if MCV and expressions don't make it.  Still, the other pieces should
be slightly easier to integrate now that the core parts have been
added.
--
Michael

--TO71gxnkcQCasJIs
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----
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=0XLh
-----END PGP SIGNATURE-----

--TO71gxnkcQCasJIs--