RE: speed up a logical replica setup

Dear Shlok,

Thanks for updating the patch!

> I have created a topup patch 0007 on top of v15-0006.
>
> I revived the patch which removes -S option and adds some options
> instead. The patch add option for --port, --username and --socketdir.
> This patch also ensures that anyone cannot connect to the standby
> during the pg_createsubscriber, by setting listen_addresses,
> unix_socket_permissions, and unix_socket_directories.

IIUC, there are two reasons why removing -S may be good:

* force users to specify a local-connection, and
* avoid connection establishment on standby during the pg_createsubscriber.

First bullet is still valid, but we should describe that like pg_upgrade:

>
pg_upgrade will connect to the old and new servers several times, so you might
want to set authentication to peer in pg_hba.conf or use a ~/.pgpass file
(see Section 33.16).
>

Regarding the second bullet, this patch cannot ensure it. pg_createsubscriber
just accepts port number which has been already accepted by the standby, it does
not change the port number. So any local applications on the standby server can
connect to the server and may change primary_conninfo, primary_slot_name, data, etc.
So...what should be? How do other think?

Beside, 0007 does not follow the recent changes on 0001. E.g., options should be
record in CreateSubscriberOptions. Also, should we check the privilege of socket
directory?

[1]: https://www.postgresql.org/message-id/TY3PR01MB988902B992A4F2E99E1385EDF56F2%40TY3PR01MB9889.jpnprd01.prod.outlook.com

Best Regards,
Hayato Kuroda
FUJITSU LIMITED
https://www.fujitsu.com/