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From: Ron Johnson <[email protected]>
To: pgsql-generallists.postgresql.org <[email protected]>
Subject: Re: In-order pg_dump (or in-order COPY TO)
Date: Tue, 26 Aug 2025 18:12:52 -0400
Message-ID: <CANzqJaCxNP9TjC9WnhaF3F_FKBmL7UXKRiQzoV5nnDS4vmbnxg@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<[email protected]>

On Tue, Aug 26, 2025 at 6:08 PM Tom Lane <[email protected]> wrote:

> Dimitrios Apostolou <[email protected]> writes:
> > Unfortunately after I did pg_restore to a new server, I notice that the
> > dumps from the new server are not being de-duplicated, all blocks are
> > considered new.
>
> > This means that the data has been significantly altered. The new dumps
> > contain the same rows but probably in very different order. Could the
> > row-order have changed when doing COPY FROM with pg_restore?
>
> I'd expect pg_dump/pg_restore to preserve the physical row ordering,
> simply because it doesn't do anything that would change that.
>
> However, restoring into an empty table would result in a table with
> minimal free space, whereas the original table probably had a
> meaningful amount of free space thanks to updates and deletes.  Thus
> for example TIDs would not be the same.  If your "rolling checksum"
> methodology is at all sensitive to page boundaries, the table would
> look quite different to it.
>

But the rolling checksums are against a pg_dump file, not a pg_basebackup
file.

What probably changed are table OIDs.  Would that change the ordering of
COPY data in post-restore dump files?

-- 
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!

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