Horton

Re: bug when apply fast default mechanism for adding new column over domain with default value

Tom Lane <tgl@sss.pgh.pa.us>

View thread View on postgr.es
From: Tom Lane <tgl@sss.pgh.pa.us>
To: jian he <jian.universality@gmail.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2025-03-01T06:43:44Z
Lists: pgsql-hackers 
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

Commits

  1. Need to do CommandCounterIncrement after StoreAttrMissingVal.

  2. Simplify some logic around setting pg_attribute.atthasdef.

  3. Remove now-dead code in StoreAttrDefault().

  4. Fix broken handling of domains in atthasmissing logic.