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help / color / mirror / Atom feedFrom: Amit Kapila <[email protected]>
To: Antonin Houska <[email protected]>
Cc: Mihail Nikalayeu <[email protected]>
Cc: Andres Freund <[email protected]>
Cc: Alvaro Herrera <[email protected]>
Cc: Srinath Reddy Sadipiralla <[email protected]>
Cc: Matthias van de Meent <[email protected]>
Cc: Pg Hackers <[email protected]>
Cc: Robert Treat <[email protected]>
Subject: Re: Adding REPACK [concurrently]
Date: Sun, 10 May 2026 17:01:04 +0530
Message-ID: <CAA4eK1KC6CGN-N2bUffSign8Sw4q6=8d3L-Xh4t+50GCdQb6zw@mail.gmail.com> (raw)
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On Tue, May 5, 2026 at 6:17 PM Antonin Houska <[email protected]> wrote:
>
> Antonin Houska <[email protected]> wrote:
>
> I think the problem is that with database-specific snapshot,
> SnapBuildProcessRunningXacts() returns early, w/o adjusting builder->xmin
>
> /*
> * Database specific transaction info may exist to reach CONSISTENT state
> * faster, however the code below makes no use of it. Moreover, such
> * record might cause problems because the following normal (cluster-wide)
> * record can have lower value of oldestRunningXid. In that case, let's
> * wait with the cleanup for the next regular cluster-wide record.
> */
> if (OidIsValid(running->dbid))
> return;
>
> and thus some transactions whose XID is below running->oldestRunningXid may
> continue to be incorrectly considered running.
>
> I originally thought that this should not happen because such transactions
> will be added to the builder's array of committed transactions by
> SnapBuildCommitTxn() anyway. However, I failed to notice that COMMIT record of
> a transaction listed in the xl_running_xacts WAL record is not guaranteed to
> follow the xl_running_xacts record in WAL. In other words, even if
> xl_running_xacts is created before a COMMIT record of the contained
> transaction, it may end up at higher LSN in WAL. So the cleanup I relied on
> might not take place.
>
BTW, is it possible to write a test by using injection_points or via
manual steps (by using debugger, etc) so that we can more clearly
understand this problem and proposed fix?
--
With Regards,
Amit Kapila.
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Subject: Re: Adding REPACK [concurrently]
In-Reply-To: <CAA4eK1KC6CGN-N2bUffSign8Sw4q6=8d3L-Xh4t+50GCdQb6zw@mail.gmail.com>
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