MIME-Version: 1.0
References: 
 <CAD21AoCTNGiddikkUcDKj5QLnsg-51bpr-o6L-GTHWZL4ZFYtQ@mail.gmail.com>
 <CALj2ACXLkU4y+mmk2gHzmvSV4KTishSe=HhZ_yn=NHFBDGrwFQ@mail.gmail.com>
 <CAA4eK1JC9+R4S7L7y3DazOOMpnANVyCpsx84RSYjX6vfxLdK6w@mail.gmail.com>
 <CAD21AoATy+CzYmNYp_fKi4zsGLEGOmZen3OR+hxsCqn2GsQBoQ@mail.gmail.com>
In-Reply-To: 
 <CAD21AoATy+CzYmNYp_fKi4zsGLEGOmZen3OR+hxsCqn2GsQBoQ@mail.gmail.com>
From: Fujii Masao <masao.fujii@gmail.com>
Date: Thu, 9 Jul 2026 21:14:46 +0900
Message-ID: 
 <CAHGQGwELqH7P8PBOGE2-un8qC_oQpT2jOgbPsAjK6YA5dnbKWQ@mail.gmail.com>
Subject: Re: Add a hook for handling logical decoding messages on subscribers.
To: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>,
	Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Archived-At: 
 <https://www.postgresql.org/message-id/CAHGQGwELqH7P8PBOGE2-un8qC_oQpT2jOgbPsAjK6YA5dnbKWQ%40mail.gmail.com>
Precedence: bulk

On Wed, Jun 24, 2026 at 3:02=E2=80=AFAM Masahiko Sawada <sawada.mshk@gmail.=
com> wrote:
> Right. I'm implementing a basic DDL replication solution using this
> hook as a sample implementation. Other than that, this feature can be
> used to add additional information for the replicated transaction that
> is not replicated via logical replication protocol, such as the
> executed user or context-specific information, which can then be
> dispatched to a CDC system connected to the subscriber.

+1 for the proposed hook, although I haven't read the patch yet.

I know of a system that uses logical decoding messages to propagate data
to external systems. In that system, the application writes the data to
be propagated as logical decoding messages, and a CDC pipeline consumes
them via logical decoding and sends them to other systems, for example
through Kafka.

In that system, when the remote site is maintained by physical replication,
the same logical decoding messages can be decoded on the standby
at the remote site to deliver them to external systems there. However,
if the remote site uses logical replication instead, those messages are
currently neither delivered to nor processed on the subscriber at
the remote site. As a result, the CDC pipeline at the remote site cannot
consume the data they carry.

The proposed hook might be useful for this use case. An extension could
process the incoming logical decoding messages on the subscriber and
forward them to the local CDC pipeline, or store or re-emit them in a form
that local consumers can process.

Regards,

--=20
Fujii Masao