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From: jian he <[email protected]>
To: Junwang Zhao <[email protected]>
Cc: David Rowley <[email protected]>
Cc: Alexander Lakhin <[email protected]>
Cc: Tender Wang <[email protected]>
Cc: Andres Freund <[email protected]>
Cc: John Naylor <[email protected]>
Cc: PostgreSQL Developers <[email protected]>
Subject: Re: More speedups for tuple deformation
Date: Wed, 1 Apr 2026 21:19:48 +0800
Message-ID: <CACJufxHzTY2ZWPy7RNCY2S-Z2A+8j7CqhKbdKrzFUhykQiTfVA@mail.gmail.com> (raw)
In-Reply-To: <CAEG8a3KNcN38Q016sAGwXWokFjj-Niq4Sy1PuGbeFQVkOP1Y6g@mail.gmail.com>
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On Wed, Apr 1, 2026 at 1:13 PM Junwang Zhao <[email protected]> wrote:
>
> 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/





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