Re: Using CTID system column as a "temporary" primary key

Laurent,

Thanks for the advice about REPEATABLE READ isolation level!

Seb
________________________________
From: Laurenz Albe <laurenz.albe@cybertec.at>
Sent: Wednesday, March 29, 2023 1:08 PM
To: Kirk Wolak <wolakk@gmail.com>; Sebastien Flaesch <sebastien.flaesch@4js.com>
Cc: Geoff Winkless <pgsqladmin@geoff.dj>; pgsql-general <pgsql-general@lists.postgresql.org>
Subject: Re: Using CTID system column as a "temporary" primary key

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On Tue, 2023-03-28 at 14:24 -0400, Kirk Wolak wrote:
>
> I cringe at the thought of using CTID.  And while it's probably "safe enough"
> inside a single transaction.  I doubt that there is much "testing" of this concept.

It is safe to assume that the CTID is stable within a single transaction
only if you use REPEATABLE READ or better transaction isolation level.

With READ COMMITTED, you see updated rows (and consequently changed CTID)
within a single transaction.  And if you use SELECT ... FOR UPDATE, you
could even see a changed CTID within a single statement.

So don't use CTID to identify rows unless you use REPEATABLE READ or better.

Yours,
Laurenz Albe