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From: Xuneng Zhou <xunengzhou@gmail.com>
Date: Thu, 9 Apr 2026 14:38:59 +0800
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Subject: Re: Bug: WAIT FOR LSN crashes with assertion failure inside PL/pgSQL
 DO blocks and procedures
To: Alexander Korotkov <aekorotkov@gmail.com>
Cc: SATYANARAYANA NARLAPURAM <satyanarlapuram@gmail.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
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On Thu, Apr 9, 2026 at 2:00=E2=80=AFPM Alexander Korotkov <aekorotkov@gmail=
.com> wrote:
>
> 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 whe=
n WAIT FOR LSN ... INTO is used inside PL/pgSQL DO blocks or within void pr=
ocedures.
> >
> > 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=
 requires 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 rev=
iew.
>
> 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.
>


--=20
Best,
Xuneng