Re: Initial COPY of Logical Replication is too slow

On Wed, Mar 18, 2026 at 1:11 PM Jan Wieck <jan(at)wi3ck(dot)info> wrote:
>
> On 3/18/26 12:44, Masahiko Sawada wrote:
> > On Wed, Mar 18, 2026 at 6:56 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >>
> >> On Tue, Mar 10, 2026 at 3:40 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> >> >
> >> > On Tue, Mar 3, 2026 at 2:22 AM Zhijie Hou (Fujitsu)
> >> > <houzj(dot)fnst(at)fujitsu(dot)com> wrote:
> >> > >
> >> > > On Saturday, February 28, 2026 7:48 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> >> > > > To: Marcos Pegoraro <marcos(at)f10(dot)com(dot)br>
> >> > > > Cc: PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
> >> > > > Subject: Re: Initial COPY of Logical Replication is too slow
> >> > > >
> >> > > > Another variant of this approach is to extend
> >> > > > pg_get_publication_table() so that it can accept a relid to get the publication
> >> > > > information of the specific table. I've attached the patch for this idea. I'm
> >> > > > going to add regression test cases.
> >> > > >
> >> > > > pg_get_publication_table() is a VARIACID array function so the patch changes
> >> > > > its signature to {text[] [, oid]}, breaking the tool compatibility. Given this
> >> > > > function is mostly an internal-use function (we don't have the documentation
> >> > > > for it), it would probably be okay with it. I find it's clearer than the other
> >> > > > approach of introducing pg_get_publication_table_info(). Feedback is very
> >> > > > welcome.
> >> > >
> >> > > Thanks for updating the patch.
> >> > >
> >> > > I have few comments for the function change:
> >> > >
> >> > > 1.
> >> > >
> >> > > If we change the function signature, will it affect use cases where the
> >> > > publisher version is newer and the subscriber version is older ? E.g., when
> >> > > publisher is passing text style publication name to pg_get_publication_tables().
> >> >
> >> > Good point.
> >> >
> >> > I noticed that changing the function signature of
> >> > pg_get_publication_tables() breaks logical replication setups where
> >> > the subscriber is 18 or older.
> >> >
> >>
> >> Why adding a new function with additional parameters (Oid relid)
> >> couldn't help with such a case? I am asking because your previous
> >> version code looks simpler as compared to the new patch version.
> >
> > I tried to pass a relid to pg_get_publication_tables() but we cannot
> > avoid changing its signature because it's a VARIADIC array function.
> > The previous patch changed pg_get_publication_tables(VARIADIC text[])
> > to pg_get_publication_tables(text[] {, relid}). However, changing the
> > function signature would break the logical replication from v19 to an
> > older version.
>
> Would it be possible to use function overloading to provide both
> signatures handled by different C functions internally?

Yes, we can define both pg_get_publication_tables(VARIADIC text[]) and
pg_get_publication_tables(text, oid), which seems like a less invasive
approach. I'll give this idea a shot and see how it goes.

Regards,

--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com