Feedback-ID: ia2694551:Fastmail
Date: Sun, 9 Apr 2023 21:11:01 +0200
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Andres Freund <andres@anarazel.de>,
	Justin Pryzby <pryzby@telsasoft.com>,
	Peter Eisentraut <peter.eisentraut@enterprisedb.com>,
	pgsql-hackers@lists.postgresql.org
Subject: Re: cataloguing NOT NULL constraints
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On 2023-Apr-09, Tom Lane wrote:

> In the new dispensation, pg_dump omits the NOT NULL clauses.
> Great, you say, that makes the output more like what the user wrote.
> I'm not so sure.  This means that the ALTER TABLE will be compelled
> to perform a full-table scan to verify that there are no nulls in the
> already-loaded data before it can add the missing NOT NULL constraint.

Yeah, I agree that this unintended consequence isn't very palatable.  I
think the other pg_upgrade problem is easily fixed (haven't tried yet),
but having to rethink the pg_dump representation would likely take
longer than we'd like.

> I'm inclined to think that this idea of suppressing the implied
> NOT NULL from PRIMARY KEY is a nonstarter and we should just
> go ahead and make such a constraint.  Another idea could be for
> pg_dump to emit the NOT NULL, load data, do the ALTER ADD PRIMARY
> KEY, and then ALTER DROP NOT NULL.

I like that second idea, yeah.  It might be tough to make it work, but
I'll try.

> In any case, I wonder whether that's the sort of redesign we should
> be doing post-feature-freeze.  It might be best to revert and try
> again in v17.

Yeah, sounds like reverting for now and retrying in v17 with the
discussed changes might be better.

-- 
Álvaro Herrera         PostgreSQL Developer  —  https://www.EnterpriseDB.com/
"La espina, desde que nace, ya pincha" (Proverbio africano)