Re: pg_upgrade and logical replication

On Sat, 25 Nov 2023 at 17:50, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Sat, Nov 25, 2023 at 7:21 AM vignesh C <vignesh21(at)gmail(dot)com> wrote:
> >
>
> Few comments on v19:
> ==================
> 1.
> + <para>
> + The subscriptions will be migrated to the new cluster in a disabled state.
> + After migration, do this:
> + </para>
> +
> + <itemizedlist>
> + <listitem>
> + <para>
> + Enable the subscriptions by executing
> + <link linkend="sql-altersubscription"><command>ALTER
> SUBSCRIPTION ... ENABLE</command></link>.
>
> The reason for this restriction is not very clear to me. Is it because
> we are using pg_dump for subscription and the existing functionality
> is doing it? If so, I think currently even connect is false.

This was done this way so that the apply worker doesn't get started
while the upgrade is happening. Now that we have set
max_logical_replication_workers to 0, the apply workers will not get
started during the upgrade process. I think now we can create the
subscriptions with the same options as the old cluster in case of
upgrade.

> 2.
> + * b) SUBREL_STATE_SYNCDONE: A relation upgraded while in this state
> + * would retain the replication origin in certain cases.
>
> I think this is vague. Can we briefly describe cases where the origins
> would be retained?

I will modify this in the next version

> 3. I think the cases where the publisher is also upgraded restoring
> the origin's LSN is of no use. Currently, I can't see a problem with
> restoring stale originLSN in such cases as we won't be able to
> distinguish during the upgrade but I think we should document it in
> the comments somewhere in the patch.

I will add a comment for this in the next version

Regards,
Vignesh