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In-Reply-To: 
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From: Matthias van de Meent <boekewurm+postgres@gmail.com>
Date: Thu, 27 Nov 2025 21:07:34 +0100
Message-ID: 
 <CAEze2WiXYx1LKr=9d7PLsZOYrGytY9AN__tFFw4p_Ysgm1-e5g@mail.gmail.com>
Subject: Re: Revisiting {CREATE INDEX, REINDEX} CONCURRENTLY improvements
To: Mihail Nikalayeu <mihailnikalayeu@gmail.com>
Cc: Sergey Sargsyan <sergey.sargsyan.2001@gmail.com>,
	=?UTF-8?Q?=C3=81lvaro_Herrera?= <alvherre@kurilemu.de>,
	Andres Freund <andres@anarazel.de>, Michael Paquier <michael@paquier.xyz>,
	PostgreSQL Hackers <pgsql-hackers@postgresql.org>,
 Andrey Borodin <amborodin86@gmail.com>,
	Melanie Plageman <melanieplageman@gmail.com>
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Precedence: bulk

On Thu, 27 Nov 2025 at 20:00, Mihail Nikalayeu
<mihailnikalayeu@gmail.com> wrote:
>
> Hello, Mathias!
>
> On Thu, Nov 27, 2025 at 7:41=E2=80=AFPM Matthias van de Meent
> <boekewurm+postgres@gmail.com> wrote:
> > I'm not sure a complete and common approach is that easy between CIC
> > and REPACK CONCURRENTLY.
>
> Yes, you're right, but I hope something like [0] may work.

While it might not break, and might not hold back other tables'
visibility horizons, it'll still hold back pruning on the table we're
acting on, and that's likely one which already had bloat issues if
you're running RIC (or REPACK).
Hence the approach with properly taking a new snapshot every so often
in CIC/RIC -- that way pruning is allowed up to a relatively recent
point in every table, including the one we're acting on; potentially
saving us from a vicious cycle where RIC causes table bloat in the
table it's working on due to long-held snapshots and a high-churn
workload in that table.


Kind regards,

Matthias van de Meent
Databricks (https://www.databricks.com)

PS. When I checked the code you linked to on that thread, I noticed
there is a stale pointer dereference issue in
GetPinnedOldestNonRemovableTransactionId, where it pulls data from a
hash table entry that could've been released by that point.