Re: pg_upgrade: optimize replication slot caught-up check

On Thu, Jan 29, 2026 at 8:31 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Fri, Jan 30, 2026 at 9:45 AM shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
> >
> > On Fri, Jan 30, 2026 at 2:15 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> > >
> > > On Wed, Jan 28, 2026 at 10:06 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > > >
> > > > On Wed, Jan 28, 2026 at 2:06 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> > > > >
> > > > > I missed fixing one place. Attached the new version.
> > > > >
> > > >
> > > > One question/comment on following change:
> > > > + bool use_fast_caught_up_check;
> > > > +
> > > > + logical_slot_infos_query = get_old_cluster_logical_slot_infos_query(cluster,
> > > > + &use_fast_caught_up_check);
> > > > +
> > > > upgrade_task_add_step(task,
> > > > logical_slot_infos_query,
> > > > process_old_cluster_logical_slot_infos,
> > > > true, NULL);
> > > > +
> > > > + /*
> > > > + * Check whether slots have consumed all WAL records efficiently by
> > > > + * using another query, if not during a live_check.
> > > > + */
> > > > + if (use_fast_caught_up_check && !user_opts.live_check)
> > > > + {
> > > >
> > > > Won't this lead to two steps to set caught_up for slots in PG19 and
> > > > following versions? If so, is it possible to use just one step even
> > > > for PG19 and following versions?
> > >
> > > Yes, it seems like a good simplification. I've updated the patch accordingly.
> > >
> >
> > At first glance it looks like a simplification, but on closer look, it
> > actually makes the code harder to follow and more prone to errors if
> > someone modifies it in the future.
> >
>
> I think that is primarily because of the way code is arranged by the
> patch. I think it would be better to construct a complete query
> separately for fast and non-fast checks. There will be some repeated
> parts but the chances of mistakes will be less and it would be easier
> to follow.

Agreed. I've updated that function accordingly.

>
> One minor point:
> * Fetch the logical replication slot information. The check whether the
> - * slot is considered caught up is done by an upgrade function. This
> - * regards the slot as caught up if we don't find any decodable changes.
> - * See binary_upgrade_logical_slot_has_caught_up().
> + * slot is considered caught up is done by an upgrade function, unless the
> + * fast check is available on the cluster.
>
> Isn't the caught up check done by an upgrade function both for fast
> and non-fast cases? If so, this comment needs to be improved to make
> it clear.

Fixed.

Regards,

--
Masahiko Sawada
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