From: Álvaro Herrera <alvherre@kurilemu.de>
To: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Matheus Alcantara <matheusssilv97@gmail.com>
Cc: Arseniy Mukhin <arseniy.mukhin.dev@gmail.com>
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: Fri, 7 Nov 2025 15:14:31 +0100
Message-ID: <202511071410.52ll56eyixx7@alvherre.pgsql> (raw)
In-Reply-To: <a8892a0e-7660-42d1-98bb-b677f6c15069@iki.fi>
One thing I noticed while testing this is that asyncQueueAddEntries()
fills the end of a page with a dummy entry, when the next notify doesn't
fit. However, this dummy entry contains a very valid TransactionId,
which the new freezing code will try to look up and freeze. I think
this is somewhat bogus -- we shouldn't even try to look up that XID in
the first place. I propose to clear it like this
@@ -1419,6 +1424,7 @@ asyncQueueAddEntries(ListCell *nextNotify)
*/
qe.length = QUEUE_PAGESIZE - offset;
qe.dboid = InvalidOid;
+ qe.xid = InvalidTransactionId;
qe.data[0] = '\0'; /* empty channel */
qe.data[1] = '\0'; /* empty payload */
}
(Line numbers do not match, because I have other local changes.)
--
Álvaro Herrera Breisgau, Deutschland — https://www.EnterpriseDB.com/
"I'm always right, but sometimes I'm more right than other times."
(Linus Torvalds)
https://lore.kernel.org/git/Pine.LNX.4.58.0504150753440.7211@ppc970.osdl.org/
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To: pgsql-hackers@postgresql.org
Cc: alvherre@kurilemu.de, hlinnaka@iki.fi, matheusssilv97@gmail.com, arseniy.mukhin.dev@gmail.com, 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: <202511071410.52ll56eyixx7@alvherre.pgsql>
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