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From: Álvaro Herrera <[email protected]>
To: Amul Sul <[email protected]>
Cc: Peter Eisentraut <[email protected]>
Cc: Ashutosh Bapat <[email protected]>
Cc: jian he <[email protected]>
Cc: PostgreSQL-development <[email protected]>
Cc: Joel Jacobson <[email protected]>
Cc: Alexandra Wang <[email protected]>
Cc: Suraj Kharage <[email protected]>
Subject: Re: NOT ENFORCED constraint feature
Date: Thu, 27 Mar 2025 15:15:25 +0100
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAAJ_b96=Y5Kwzx5QK4UU=BPK0F-4hBc+T-Je6FdSb2RQkyBu-g@mail.gmail.com>

On 2025-Mar-27, Amul Sul wrote:

> On Thu, Mar 27, 2025 at 6:28 PM Peter Eisentraut <[email protected]> wrote:

> > That said, is there a simpler way?  Patch 0003 appears to add a lot of
> > complexity.  Could we make this simpler by saying, if you have otherwise
> > matching constraints with different enforceability, make this an error.
> > Then users can themselves adjust the enforceability how they want to
> > make it match.
> 
> We can simply discard this patch, as it still reflects the correct
> behavior. It creates a new constraint without affecting the existing
> constraint with differing enforceability on the child. I noticed
> similar behavior with deferrability -- when it differs, the
> constraints are not merged, and a new constraint is created on the
> child. Let me know your thoughts so I can avoid squashing patch 0006.

I didn't read that patch and I don't know what level of complexity we're
talking about, but the idea of creating a second constraint beside an
existing one itches me.  I'm pretty certain most users would rather not
end up with redundant constraints that only differ in enforceability or
whatever other properties.  I failed to realize that this was happening
when adding FKs on partitioned tables, and I now think it was a mistake.
(As I said in some previous thread, I'd rather have this kind of
situation raise an error so that the user can do something about it,
rather than silently moving ahead with a worse solution like creating a
redundant constraint.)

-- 
Álvaro Herrera         PostgreSQL Developer  —  https://www.EnterpriseDB.com/
"After a quick R of TFM, all I can say is HOLY CR** THAT IS COOL! PostgreSQL was
amazing when I first started using it at 7.2, and I'm continually astounded by
learning new features and techniques made available by the continuing work of
the development team."
Berend Tober, http://archives.postgresql.org/pgsql-hackers/2007-08/msg01009.php

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