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From: Alexander Korotkov <aekorotkov@gmail.com>
Date: Thu, 9 Apr 2026 09:00:06 +0300
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 <CAPpHfdsZ6YrzX-5uenwvw1VXuG7mpBXSOT6JFTg6aCCC0SaNEg@mail.gmail.com>
Subject: Re: Bug: WAIT FOR LSN crashes with assertion failure inside PL/pgSQL
 DO blocks and procedures
To: SATYANARAYANA NARLAPURAM <satyanarlapuram@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
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Hi, Satya!

On Thu, Apr 9, 2026 at 5:03=E2=80=AFAM SATYANARAYANA NARLAPURAM
<satyanarlapuram@gmail.com> wrote:
> An assertion failure (server crash in assert-enabled builds) occurs when =
WAIT FOR LSN ... INTO is used inside PL/pgSQL DO blocks or within void proc=
edures.
>
> Repro:
>
> -- Run this on a standby
>
> CREATE PROCEDURE test_wait()
>   LANGUAGE plpgsql AS $$
>   DECLARE
>     result text;
>   BEGIN
>     WAIT FOR LSN '0/1234' INTO result;
>     RAISE NOTICE '%', result;
>   END;
>   $$;
>   CALL test_wait();
>
>
> The WAIT FOR itself succeeds, but the very next PL/pgSQL statement that r=
equires a snapshot crashes the backend with:
>
>   TRAP: failed Assert("portal->portalSnapshot =3D=3D NULL"),
>   File: "pquery.c", Line: 1776
>
> Attached patches for both the test case and a potential fix. Please revie=
w.

Thank you for reporting.  But I doubt the fix is correct.  Even that
this particular might work OK, I don't think it's safe to release
snapshots belonging to functions/procedures: it might affect them.  I
tend to think we must forbid wrapping WAIT FOR LSN with
functions/procedures.  I'll explore more on this today.

------
Regards,
Alexander Korotkov
Supabase