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

Hi, Satya!

On Thu, Apr 9, 2026 at 5:03 AM SATYANARAYANA NARLAPURAM
<satyanarlapuram(at)gmail(dot)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.

------
Regards,
Alexander Korotkov
Supabase