Re: Documentation update of wal_retrieve_retry_interval to mention table sync worker

On Tue, 31 Dec 2024 at 02:48, Peter Smith <smithpb2250@gmail.com> wrote:
>
> On Thu, Dec 26, 2024 at 1:37 AM vignesh C <vignesh21@gmail.com> wrote:
> >
> > Hi,
> >
> > Currently, we restart the table synchronization worker after the
> > duration specified by wal_retrieve_retry_interval following the last
> > failure. While this behavior is documented for apply workers, it is
> > not mentioned for table synchronization workers. I believe this detail
> > should be included in the documentation for table synchronization
> > workers as well. Attached is a patch to address this omission.
> >
> > Regards,
> > Vignesh
>
> Hi Vignesh,
>
> Here are some review comments for your v1 patch.
>
> +1 to enhance the documentation.
>
> ======
>
> 1.
>         <para>
>          In logical replication, this parameter also limits how often a failing
> -        replication apply worker will be respawned.
> +        replication apply worker, and table synchronization worker will be
> +        respawned.
>         </para>
>
> /, and/or/
>
>
> SUGGESTION
> In logical replication, this parameter also limits how often a failing
> replication apply worker or table synchronization worker will be
> respawned.

Modified

> ======
>
> 2.
> I think the reader might never be aware of any of this (throttled
> relaunch) behaviour unless they accidentally stumble across the docs
> for this GUC, so IMO this information should be mentioned elsewhere --
> wherever the tablesync worker errors are documented. But, TBH, I can't
> find anywhere in the PostgreSQL docs where it even mentions
> re-launching failed tablesync workers!
>
> Anyway, I think it might be good to include such information in some
> suitable place (maybe in the CREATE SUBSCRIPTION notes? or maybe in
> Chapter 29?) to say something like...
>
> SUGGESTION:
> In practice, if a table synchronization worker fails during logical
> replication, the apply worker detects the failure and attempts to
> respawn the table synchronization worker to continue the
> synchronization process. This behaviour ensures that transient errors
> do not permanently disrupt the replication setup. See also
> wal_retrieve_retry_interval.

Yes, adding it to logical replication Initial Snapshot seemed more
appropriate to me.

The attached v2 version patch has the changes for the same.

Regards,
Vignesh