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From: Amit Kapila <[email protected]>
To: Andres Freund <[email protected]>
Cc: Alvaro Herrera <[email protected]>
Cc: Mihail Nikalayeu <[email protected]>
Cc: Antonin Houska <[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: Wed, 8 Apr 2026 14:05:49 +0530
Message-ID: <CAA4eK1JDrk9xiALd4DHnGLOkGDbObM59SXSBJyj0_1bNYbr5ng@mail.gmail.com> (raw)
In-Reply-To: <4n4q3preb3lgyhpzstebhux7b2aojhsw7gik4ivaznyggiezrs@lrznutssxlh2>
References: <CADzfLwWFr9h_+cbSQvPpdxgLbVL5wwxFRx21ezNvLYgJM=FVCQ@mail.gmail.com>
	<[email protected]>
	<4n4q3preb3lgyhpzstebhux7b2aojhsw7gik4ivaznyggiezrs@lrznutssxlh2>

On Wed, Apr 8, 2026 at 1:54 AM Andres Freund <[email protected]> wrote:
>
> Hi,
>
> On 2026-04-07 00:22:32 +0200, Alvaro Herrera wrote:
> > From 4303eea0a72408183f9f5afcf8d2801df20f8ffe Mon Sep 17 00:00:00 2001
> > From: Antonin Houska <[email protected]>
> > Date: Wed, 1 Apr 2026 17:35:47 +0200
> > Subject: [PATCH v56 3/3] Error out any process that would block at REPACK
> >
> > Any process waiting on REPACK to release its lock would actually cause
> > it to deadlock when it tries to upgrade its lock to AEL, losing all work
> > done to that point.  We avoid this by teaching the deadlock detector to
> > raise an error when this condition is detected.
>
> I'm rather doubtful that that is ok.
>

Another possible idea is that after copying table_data to the new
table, we mark the old table as in_use_by_repack and release the
ShareUpdateExclusiveLock on the old table. Then the function
CheckTableNotInUse() should be updated to give an ERROR if the table
is marked as in_use_by_repack. Now, acquiring AEL by repack
(concurrently) should be safe because all concurrent DDLs should be
errored out due to flag in_use_by_repack. Can this address the problem
we are worried about the lock upgrade?

-- 
With Regards,
Amit Kapila.

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