Feedback-ID: ia2694551:Fastmail
Date: Wed, 25 Feb 2026 17:25:54 +0100
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Antonin Houska <ah@cybertec.at>
Cc: Mihail Nikalayeu <mihailnikalayeu@gmail.com>,
	Pg Hackers <pgsql-hackers@lists.postgresql.org>,
 Robert Treat <rob@xzilla.net>
Subject: Re: Adding REPACK [concurrently]
Message-ID: <202602251618.dpgvox64vziz@alvherre.pgsql>
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On 2026-Feb-25, Antonin Houska wrote:

> > Hmm, so on the apply side when reading the file, we would first reach
> > each toast attribute value, which we know to insert directly to the
> > toast table (keeping track of each individually toast pointer as we do
> > so); then we reach the heap tuple itself, we [... somehow ...] interpret
> > these external indirect toast pointers and substitute the toast pointers
> > that we created.  So we never have to construct the entire tuple, or
> > indeed do anything else with the toasted values other than insert them
> > into the toast table.
> 
> Yes, that's what I mean.

Makes sense.  Would you be able to try and implement that?

> The problem I see here is that for UPDATE you need the old tuple to determine
> if its TOAST value should be deleted or if the new tuple should reuse it -
> this is how I understand toast_tuple_init(). So the worker would have to store
> all the changes somewhere temporarily until it can fully apply the changes
> (i.e. until the initial copy and index build is complete).

Ah, you're right, that won't work.

-- 
Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/
Tom: There seems to be something broken here.
Teodor: I'm in sackcloth and ashes...  Fixed.
                               http://postgr.es/m/482D1632.8010507@sigaev.ru