Re: Bug: WAIT FOR LSN crashes with assertion failure inside PL/pgSQL DO blocks and procedures

Hi Alexander,

On Thu, Apr 9, 2026 at 5:28 AM Alexander Korotkov <aekorotkov@gmail.com>
wrote:

> On Thu, Apr 9, 2026 at 10:27 AM SATYANARAYANA NARLAPURAM
> <satyanarlapuram@gmail.com> wrote:
> > On Wed, Apr 8, 2026 at 11:00 PM Alexander Korotkov <aekorotkov@gmail.com>
> wrote:
> >> On Thu, Apr 9, 2026 at 5:03 AM 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
> procedures.
> >> >
> >> > 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 == NULL"),
> >> >   File: "pquery.c", Line: 1776
> >> >
> >> > Attached patches for both the test case and a potential fix. Please
> review.
> >>
> >> 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.
> >
> >
> > Agreed, attached a v2 patch with your suggestion on preventing it running
> > from procedures.
>
> Thank you.  I've slightly revised your patch.  I'm going to push it if
> no objections.
>

LGTM, thank you!