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In-Reply-To: <31d12caf-17d8-4ab7-af58-ec3c5a310a92@dunslane.net>
From: jian he <jian.universality@gmail.com>
Date: Thu, 12 Mar 2026 11:36:19 +0800
Message-ID: 
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Subject: Re: support fast default for domain with constraints
To: Andrew Dunstan <andrew@dunslane.net>, Viktor Holmberg <v@viktorh.net>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
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On Thu, Mar 12, 2026 at 3:50=E2=80=AFAM Andrew Dunstan <andrew@dunslane.net=
> wrote:
> Also added some tests.

V11 looks good to me.


On Wed, Mar 11, 2026 at 6:34=E2=80=AFPM Viktor Holmberg <v@viktorh.net> wro=
te:
>
> I=E2=80=99ve been burned my this issue in the past so would be great if t=
his could get in.
>
> + /*
> + * If the domain has volatile constraints, we must do a table rewrite
> + * since the constraint result could differ per row and cannot be
> + * evaluated once and cached as a missing value.
> + */
> + if (has_volatile)
> + {
> + Assert(has_domain_constraints);
> + tab->rewrite |=3D AT_REWRITE_DEFAULT_VAL;
> + }
>
> I'm not sure. But seems to me this makes the pre-existing guard for virtu=
al columns
> redundant?
> I mean this code on line 7633:
> if (colDef->generated !=3D ATTRIBUTE_GENERATED_VIRTUAL)
>  tab->rewrite |=3D AT_REWRITE_DEFAULT_VAL;
>

If the first `if (has_volatile)` is false, then
> if (colDef->generated !=3D ATTRIBUTE_GENERATED_VIRTUAL)
>  tab->rewrite |=3D AT_REWRITE_DEFAULT_VAL;
is still reachable.

> Also, perhaps virtual generated columns could use a test?

Virtual generated columns based on domain are not currently supported.
I have a patch for it: https://commitfest.postgresql.org/patch/5725
but it's not doable now because of
https://git.postgresql.org/cgit/postgresql.git/commit/?id=3D0cd69b3d7ef357f=
2b43258de5831c4de0bd51dec
You may also be interested in https://commitfest.postgresql.org/patch/5907


--
jian
https://www.enterprisedb.com/