Re: speed up a logical replica setup

On Thu, Feb 8, 2024, at 12:04 AM, Hayato Kuroda (Fujitsu) wrote:
> >
> Remember the target server was a standby (read only access). I don't expect an
> application trying to modify it; unless it is a buggy application.
> >
>
> What if the client modifies the data just after the promotion?
> Naively considered, all the changes can be accepted, but are there any issues?

If someone modifies data after promotion, fine; she has to deal with conflicts,
if any. IMO it is solved adding one or two sentences in the documentation.

> >
> Regarding
> GUCs, almost all of them is PGC_POSTMASTER (so it cannot be modified unless the
> server is restarted). The ones that are not PGC_POSTMASTER, does not affect the
> pg_createsubscriber execution [1].
> >
>
> IIUC, primary_conninfo and primary_slot_name is PGC_SIGHUP.

Ditto.

> >
> I'm just pointing out that this case is a different from pg_upgrade (from which
> this idea was taken). I'm not saying that's a bad idea. I'm just arguing that
> you might be preventing some access read only access (monitoring) when it is
> perfectly fine to connect to the database and execute queries. As I said
> before, the current UI allows anyone to setup the standby to accept only local
> connections. Of course, it is an extra step but it is possible. However, once
> you apply v16-0007, there is no option but use only local connection during the
> transformation. Is it an acceptable limitation?
> >
>
> My remained concern is written above. If they do not problematic we may not have
> to restrict them for now. At that time, changes
>
> 1) overwriting a port number,
> 2) setting listen_addresses = ''

It can be implemented later if people are excited by it.

> are not needed, right? IIUC inconsistency of -P may be still problematic.

I still think we shouldn't have only the transformed primary_conninfo as
option.

> >
> pglogical_create_subscriber does nothing [2][3].
> >
>
> Oh, thanks.
> Just to confirm - pglogical set shared_preload_libraries to '', should we follow or not?

The in-core logical replication does not require any library to be loaded.

--
Euler Taveira
EDB https://www.enterprisedb.com/