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From: Tom Lane <[email protected]>
To: jian he <[email protected]>
Cc: PostgreSQL-development <[email protected]>
Subject: Re: support fast default for domain with constraints
Date: Tue, 04 Mar 2025 22:13:40 -0500
Message-ID: <[email protected]> (raw)
In-Reply-To: <CACJufxE_+iZBR1i49k_AHigppPwLTJi6km8NOsC7FWvKdEmmXg@mail.gmail.com>
References: <CACJufxE_+iZBR1i49k_AHigppPwLTJi6km8NOsC7FWvKdEmmXg@mail.gmail.com>

jian he <[email protected]> writes:
> Thanks to commit aaaf9449ec6be62cb0d30ed3588dc384f56274bf[1],
> ExprState.escontext (ErrorSaveContext) was added, and ExecEvalConstraintNotNull,
> ExecEvalConstraintCheck were changed to use errsave instead of hard error.
> Now we can use it to evaluate CoerceToDomain in a soft error way, that
> is what this patch intended to do.

This patch appears to summarily throw away a couple of
backwards-compatibility concerns that the previous round
took care to preserve:

* not throwing an error if the default would fail the domain
constraints, but the table is empty so there is no need to
instantiate the default.

* not assuming that the domain constraints are immutable.

Now it's fair to question how important the second point is
considering that we mostly treat domain constraints as immutable
elsewhere.  But I think the first point has actual practical uses
--- for example, if you want to set things up so that inserts must
specify that column explicitly.  So I don't think it's okay to
discard that behavior.

Maybe we need a regression test case demonstrating that that
behavior exists, to discourage people from breaking it ...

			regards, tom lane

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