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From: jian he <[email protected]>
To: Chao Li <[email protected]>
Cc: Postgres hackers <[email protected]>
Cc: Peter Eisentraut <[email protected]>
Subject: Re: Fix SET EXPRESSION for virtual columns with whole-row dependencies
Date: Sat, 13 Jun 2026 10:42:46 +0800
Message-ID: <CACJufxHaErSjsxkhMJVS9zuGvrgej831ibieAvn1+1o-GQ8dFg@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<CACJufxHTK0Qk7AwdrHK=y8OtK--zEVY-Ossxx4UUgxaE2NCAXA@mail.gmail.com>
	<[email protected]>
	<[email protected]>

On Wed, Jun 10, 2026 at 5:06 PM Chao Li <[email protected]> wrote:
>
>
> After reading the other implementation in [1], I realized that I had missed the partial-index case, so I added coverage for that.
>
> I am still sending an updated version of this patch because my implementation is different from the one in [1]. I would like people to compare the two approaches and decide which direction is better.
>

I tried your patch before but abandoned it due to many regression test failures.

RememberAllDependentForRebuilding
{
            default:
                /*
                 * We don't expect any other sorts of objects to depend on a
                 * column.  A whole-relation scan can find the relation's row
                 * type, which doesn't need rebuilding for SET EXPRESSION.
                 */
                if (attnum == 0 &&
                    foundObject.classId == TypeRelationId &&
                    get_typ_typrelid(foundObject.objectId) ==
RelationGetRelid(rel))
                    continue;
                elog(ERROR, "unexpected object depending on column: %s",
                     getObjectDescription(&foundObject, false));
                break;
}

RememberAllDependentForRebuilding(tab, AT_SetExpression, rel, 0, NULL) scans for
all dependencies on the relation (not just a specific column, since attnum=0).
This is much broader than a column-level scan.

The above DEFAULT branch in the SWITCH currently only exempts the relation's own
row type (TypeRelationId). But a table can have many other kinds of dependents
— indexes, triggers, foreign keys, views, etc. — and any of them that
hitting this
DEFAULT branch would incorrectly fire:

elog(ERROR, "unexpected object depending on column: %s", ...)

We need to check that every possible object type that can depend on a relation
and ensure none of them fall through to that `elog(ERROR, ...)`.

In RememberAllDependentForRebuilding, we have `if (subtype ==
AT_AlterColumnType)` guards against AT_SetExpression, — those branches
silently skip AT_SetExpression, which is good.
But the real risk is the DEFAULT branch, which lacks such a guard and
will error on anything unexpected.

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  Subject: Re: Fix SET EXPRESSION for virtual columns with whole-row dependencies
  In-Reply-To: <CACJufxHaErSjsxkhMJVS9zuGvrgej831ibieAvn1+1o-GQ8dFg@mail.gmail.com>

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