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From: wang.xiao.peng <[email protected]>
To: Alexander Korotkov <[email protected]>
Cc: SATYANARAYANA NARLAPURAM <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Cc: PostgreSQL-development <[email protected]>
Subject: Re:Re: Bug: WAIT FOR LSN crashes with assertion failure inside PL/pgSQL DO blocks and procedures
Date: Fri, 10 Apr 2026 07:44:54 +0800 (CST)
Message-ID: <[email protected]> (raw)
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At 2026-04-09 20:28:16, "Alexander Korotkov" <[email protected]> wrote:
>On Thu, Apr 9, 2026 at 10:27 AM SATYANARAYANA NARLAPURAM
><[email protected]> wrote:
>> On Wed, Apr 8, 2026 at 11:00 PM Alexander Korotkov <[email protected]> wrote:
>>> On Thu, Apr 9, 2026 at 5:03 AM SATYANARAYANA NARLAPURAM
>>> <[email protected]> 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.
>
>------
>Regards,
>Alexander Korotkov

>Supabase


Hi,
This patch looks good to me overall. I spotted a typo in the commit message:


"it could pass this check causing an error elsewhere.  This commit implments"


implments -> implements, missing an "e".


Regard,
Xiaopeng Wang

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