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From: jian he <jian.universality@gmail.com>
Date: Wed, 1 Apr 2026 21:19:48 +0800
Message-ID: 
 <CACJufxHzTY2ZWPy7RNCY2S-Z2A+8j7CqhKbdKrzFUhykQiTfVA@mail.gmail.com>
Subject: Re: More speedups for tuple deformation
To: Junwang Zhao <zhjwpku@gmail.com>
Cc: David Rowley <dgrowleyml@gmail.com>,
 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 1:13=E2=80=AFPM Junwang Zhao <zhjwpku@gmail.com> wro=
te:
>
> 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.
>
HI.

You can also trigger it via:

SELECT row_to_json(('', ''));

In transformRowExpr, we can coerce these UNKNOWNOID Const to TEXTOID Const.
But I guess it's harder to guarantee that comment "cstrings don't
exist in heap tuples." in nocachegetattr to be true.


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