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From: Junwang Zhao <zhjwpku@gmail.com>
Date: Wed, 1 Apr 2026 13:13:30 +0800
Message-ID: 
 <CAEG8a3KNcN38Q016sAGwXWokFjj-Niq4Sy1PuGbeFQVkOP1Y6g@mail.gmail.com>
Subject: Re: More speedups for tuple deformation
To: David Rowley <dgrowleyml@gmail.com>
Cc: Alexander Lakhin <exclusion@gmail.com>, Tender Wang <tndrwang@gmail.com>,
	Andres Freund <andres@anarazel.de>, John Naylor <johncnaylorls@gmail.com>,
	PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
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On Wed, Apr 1, 2026 at 11:35=E2=80=AFAM David Rowley <dgrowleyml@gmail.com>=
 wrote:
>
> On Wed, 1 Apr 2026 at 15:00, Alexander Lakhin <exclusion@gmail.com> wrote=
:
> > I've also found an assertion failure:
> > SELECT JSON_ARRAY(VALUES (('', '')));
> >
> > triggers:
> > TRAP: failed Assert("attlen > 0 || attlen =3D=3D -1"), File: "heaptuple=
.c", Line: 598, PID: 2582495
> >
> > Could you have a look, please?
>
> Thanks. Looking...

The parser transforms '' (or any cstring) into Const with UNKNOWNOID.
When building the tuple descriptor in ExecTypeFromExprList,
TupleDescInitEntry uses UNKNOWNOID to populate the attribute entry,
thus the failure in nocachegetattr.

Therefore, the assertion should be addressed by removing the pg_assume,
since this case can occur.

Just trying to learn through analysis, might be incorrect. Let's wait for
David's fix.

>
> David
>
>


--=20
Regards
Junwang Zhao