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From: Antonin Houska <[email protected]>
To: [email protected]
Subject: Re: Race conditions in logical decoding
Date: Tue, 20 Jan 2026 09:30:33 +0100
Message-ID: <62335.1768897833@localhost> (raw)
In-Reply-To: <85833.1768840165@localhost>
References: <85833.1768840165@localhost>

Antonin Houska <[email protected]> wrote:

> I'm not sure yet how to fix the problem. I tried to call XactLockTableWait()
> from SnapBuildAddCommittedTxn() (like it happens in SnapBuildWaitSnapshot()),
> but it made at least one regression test (subscription/t/010_truncate.pl)
> stuck - probably a deadlock. I can spend more time on it, but maybe someone
> can come up with a good idea sooner than me.

Attached here is what I consider a possible fix - simply wait for the CLOG
update before building a new snapshot.

Unfortunately I have no idea right now how to test it using the isolation
tester. With the fix, the additional waiting makes the current test
block. (And if a step is added that unblock the session, it will not reliably
catch failure to wait.)

-- 
Antonin Houska
Web: https://www.cybertec-postgresql.com



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