From: Tom Lane <tgl@sss.pgh.pa.us>
To: jian he <jian.universality@gmail.com>
cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: bug when apply fast default mechanism for adding new column over
 domain with default value
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Comments: In-reply-to jian he <jian.universality@gmail.com>
	message dated "Sat, 01 Mar 2025 13:39:56 +0800"
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Date: Sat, 01 Mar 2025 01:43:44 -0500
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jian he <jian.universality@gmail.com> writes:
> then I think I found a bug for applying fast default over domain with
> default value.

Yeah, that's definitely a bug: it worked correctly in versions
before we invented the attmissingval mechanism.

> column b type is domain int_domain3, which has a constraint.
> As a result, adding column b triggers a table rewrite, ensuring the
> domain default value is successfully applied.

I do not believe that case should require a table rewrite.
Both the default and the check constraint are immutable,
so we ought to be able to apply the check once and then
use the default as the attmissingval.

> Attach a patch to fix this issue by cause it to table rewrite.

I see no attached patch, but in any case forcing a table rewrite
seems like the wrong direction...

			regards, tom lane