Message-ID: <5edd4f4a-0d79-465d-a250-8b4735f780ca@gmail.com>
Date: Fri, 5 Jun 2026 08:00:00 +0300
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: BUG #18158: Assert in pgstat_report_stat() fails when a backend
 shutting down with stats pending
To: Michael Paquier <michael@paquier.xyz>, Xuneng Zhou <xunengzhou@gmail.com>
Cc: pgsql-bugs@lists.postgresql.org
References: <18158-88f667028dbc7e7b@postgresql.org>
 <58b5d6bf-7dca-41e5-8000-e12981205ada@gmail.com>
 <CABPTF7XdDoLAoLKo7pOHmSqHniHf46Pw8Z=iqNx2uYi4J5ixBA@mail.gmail.com>
 <agQgZKF6q3rYRX7O@paquier.xyz>
 <CABPTF7VgzdBP_ZPKf2eZ79ry0fVKzcgCkB5gy60HGXCy0EQb0w@mail.gmail.com>
 <aiIxB2oawj8pZeON@paquier.xyz>
Content-Language: en-US
From: Alexander Lakhin <exclusion@gmail.com>
In-Reply-To: <aiIxB2oawj8pZeON@paquier.xyz>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Archived-At: 
 <https://www.postgresql.org/message-id/5edd4f4a-0d79-465d-a250-8b4735f780ca%40gmail.com>
Precedence: bulk

Hello Michael,

05.06.2026 05:14, Michael Paquier wrote:
> On Thu, May 14, 2026 at 03:19:34PM +0800, Xuneng Zhou wrote:
>> I agree that applying the change wholesale could be too invasive. If
>> we decide not to address the ordering issue, removing this assertion
>> seems reasonable, since the non-assert path does not actually provide
>> the required guarantee.
> Attached is a patch for 15~17 that is able to achieve this goal:
> - Lift the assertion on shutdown for WAL senders, but keep it
> everywhere else.
> - Secondary trick in pgstat_shutdown_hook to cope with the fact that
> some stats make still be around at shutdown for a WAL sender.
>
> I cannot reproduce the failure re-using the trick sent by Alexander at
> the top of the thread.

Please try the following:
--- a/src/backend/utils/activity/pgstat.c
+++ b/src/backend/utils/activity/pgstat.c
@@ -107,2 +107,3 @@

+#include "common/pg_prng.h"

@@ -1212,3 +1213,8 @@ pgstat_flush_pending_entries(bool nowait)
          /* flush the stats, if possible */
+if (nowait && (pg_prng_double(&pg_global_prng_state) < 0.1))
+        did_flush = false;
+else
+{
          did_flush = kind_info->flush_pending_cb(entry_ref, nowait);
+}

As far as I can see, that rand() gives the same sequence on macOS each run,
while on Linux I see different sequences.

The patch works for me test-wise.

Thank you for the fix!

Best regards,
Alexander