From: Álvaro Herrera <alvherre@kurilemu.de>
To: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Joel Jacobson <joel@compiler.org>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: LISTEN/NOTIFY bug: VACUUM sets frozenxid past a xid in async queue
Date: Tue, 4 Nov 2025 17:27:48 +0100
Message-ID: <202511041624.uthdnt3tzhm2@alvherre.pgsql> (raw)
In-Reply-To: <66213fee-00ff-4952-802d-c06454e521ac@iki.fi>
On 2025-Nov-04, Heikki Linnakangas wrote:
> From 7c342e6efffc8d59c2e7658f6f2f3b138d02e0bb Mon Sep 17 00:00:00 2001
> From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
> Date: Tue, 4 Nov 2025 13:22:08 +0200
> Subject: [PATCH v2 1/2] Fix bug where we truncated CLOG that was still needed
> by LISTEN/NOTIFY
> The async notification queue contains the XID of the sender, and when
> processing notifications we call TransactionIdDidCommit() on the
> XID. But we had no safeguards to prevent the CLOG segments containing
> those XIDs from being truncated away. As a result, if a backend didn't
> for some reason process its notifications for a long time, or when a
> new backend issued LISTEN, you could get an error like:
>
> test=# listen c21;
> ERROR: 58P01: could not access status of transaction 14279685
> DETAIL: Could not open file "pg_xact/000D": No such file or directory.
> LOCATION: SlruReportIOError, slru.c:1087
>
> Note: This commit is not a full fix. [...]
The commit message doesn't say just _what_ does the patch do to fix the
bug though. Looking through the code, I think you're setting XIDs in
the async queue to frozenXid, but I think the commit message should
explain that.
Thanks for spending time on this.
--
Álvaro Herrera Breisgau, Deutschland — https://www.EnterpriseDB.com/
"La fuerza no está en los medios físicos
sino que reside en una voluntad indomable" (Gandhi)
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-hackers@postgresql.org
Cc: alvherre@kurilemu.de, hlinnaka@iki.fi, joel@compiler.org, tgl@sss.pgh.pa.us
Subject: Re: LISTEN/NOTIFY bug: VACUUM sets frozenxid past a xid in async queue
In-Reply-To: <202511041624.uthdnt3tzhm2@alvherre.pgsql>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox