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From: shveta malik <shveta.malik@gmail.com>
Date: Tue, 20 Jan 2026 16:08:33 +0530
Message-ID: <CAJpy0uAR_3YzA8fXHGnnZN8GLDBwPpQ=VJD5478GaTPQ5gMYhg@mail.gmail.com>
Subject: Re: Proposal: Conflict log history table for Logical Replication
To: Dilip Kumar <dilipbalaut@gmail.com>
Cc: Peter Smith <smithpb2250@gmail.com>, vignesh C <vignesh21@gmail.com>, 
	Amit Kapila <amit.kapila16@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, 
	Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>, 
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, shveta malik <shveta.malik@gmail.com>
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Archived-At: <https://www.postgresql.org/message-id/CAJpy0uAR_3YzA8fXHGnnZN8GLDBwPpQ%3DVJD5478GaTPQ5gMYhg%40mail.gmail.com>
Precedence: bulk

On Tue, Jan 13, 2026 at 4:09=E2=80=AFPM Dilip Kumar <dilipbalaut@gmail.com>=
 wrote:
>
> On Tue, Jan 13, 2026 at 3:59=E2=80=AFPM shveta malik <shveta.malik@gmail.=
com> wrote:
> >
> > 1)
> > I am able to insert and update rows in pg_conflict.pg_conflict_16394.
> > It should be restricted.
> >
> > 2)
> > I think we need to block 'SELECT for UPDATE' and similar operations on
> > CLT. Currently it is allowed on CLT.
> > See this:
> >
> > postgres=3D# SELECT * FROM  pg_toast.pg_toast_3466 for UPDATE;
> > ERROR:  cannot lock rows in TOAST relation "pg_toast_3466"
> > postgres=3D# SELECT * FROM pg_conflict.pg_conflict_16394 for UPDATE;
> > ....
>

I had a quick look at v23-001, I see that it has INSERT and UPDATE
blocked but SELECt for UPDATE is still working. I do not see any
strong need to provide this flexibility for user-level concurrency
control on conflict-tables. Shall this be blocked as well?

Also, the error I get for INSERT and UPDATE is:

postgres=3D# update pg_conflict.pg_conflict_16390 set relid=3D1;
ERROR:  cannot modify or insert data for conflict log table "pg_conflict_16=
390"
DETAIL:  Conflict log tables are system-managed and only support
cleanup via DELETE or TRUNCATE.

I feel "cannot modify or insert data into conflict log table ..."
seems more natural.

thanks
Shveta