From: Antonin Houska <ah@cybertec.at>
To: Mihail Nikalayeu <mihailnikalayeu@gmail.com>
cc: Alvaro Herrera <alvherre@alvh.no-ip.org>,
    Fujii Masao <masao.fujii@gmail.com>, Robert Treat <rob@xzilla.net>,
    Pg Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Adding REPACK [concurrently]
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Comments: In-reply-to Mihail Nikalayeu <mihailnikalayeu@gmail.com>
   message dated "Mon, 25 Aug 2025 20:18:17 +0200."
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Date: Tue, 26 Aug 2025 10:46:00 +0200
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Mihail Nikalayeu <mihailnikalayeu@gmail.com> wrote:

> Antonin Houska <ah@cybertec.at>:
> > I think the problem is that HeapTupleSatisfiesSelf() uses
> > TransactionIdIsInProgress() instead of checking the snapshot:
> =

> Yes, some issues might be possible for SnapshotSelf.
> Possible solution is to override TransactionIdIsCurrentTransactionId
> to true (like you did with nParallelCurrentXids but just return true).
> IIUC, in that case all checks are going to behave the same way as in v5 =
version.

I assume you mean v12-0005. Yes, that modifies
TransactionIdIsCurrentTransactionId(), so that the the transaction being
replayed recognizes if it (or its subtransaction) performed particular cha=
nge
itself.

Although it could work, I think it'd be confusing to consider the transact=
ions
being replayed as "current" from the point of view of the backend that
executes REPACK CONCURRENTLY.

But the primary issue is that in v12-0005,
TransactionIdIsCurrentTransactionId() gets the information on "current
transactions" from snapshots - see the calls of SetRepackCurrentXids() bef=
ore
each scan. It's probably not what you want.

-- =

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