Re: speed up a logical replica setup

Hi,

On Tue, 20 Feb 2024 at 06:59, Euler Taveira <euler(at)eulerto(dot)com> wrote:
>
> On Mon, Feb 19, 2024, at 7:22 AM, Shlok Kyal wrote:
>
> I have reviewed the v21 patch. And found an issue.
>
> Initially I started the standby server with a new postgresql.conf file
> (not the default postgresql.conf that is present in the instance).
> pg_ctl -D ../standby start -o "-c config_file=/new_path/postgresql.conf"
>
> And I have made 'max_replication_slots = 1' in new postgresql.conf and
> made 'max_replication_slots = 0' in the default postgresql.conf file.
> Now when we run pg_createsubscriber on standby we get error:
> pg_createsubscriber: error: could not set replication progress for the
> subscription "pg_createsubscriber_5_242843": ERROR: cannot query or
> manipulate replication origin when max_replication_slots = 0
>
>
> That's by design. See [1]. The max_replication_slots parameter is used as the
> maximum number of subscriptions on the server.
>
> NOTICE: dropped replication slot "pg_createsubscriber_5_242843" on publisher
> pg_createsubscriber: error: could not drop publication
> "pg_createsubscriber_5" on database "postgres": ERROR: publication
> "pg_createsubscriber_5" does not exist
> pg_createsubscriber: error: could not drop replication slot
> "pg_createsubscriber_5_242843" on database "postgres": ERROR:
> replication slot "pg_createsubscriber_5_242843" does not exist
>
>
> That's a bug and should be fixed.
>
> [1] https://www.postgresql.org/docs/current/runtime-config-replication.html#RUNTIME-CONFIG-REPLICATION-SUBSCRIBER
>
I think you misunderstood the issue, I reported.

My main concern is that the standby server is using different
'postgresql.conf' file (the default file) after :
+ /* Start subscriber and wait until accepting connections */
+ pg_log_info("starting the subscriber");
+ if (!dry_run)
+ start_standby_server(pg_ctl_path, opt.subscriber_dir, server_start_log);

But we initially started the standby server (before running the
pg_createsubscriber) with a new postgresql.conf file (different from
the default file. for this example created inside the 'new_path'
folder).
pg_ctl -D ../standby -l standby.log start -o "-c
config_file=../new_path/postgresql.conf"

So, when we run the pg_createsubscriber, all the initial checks will
be run on the standby server started using the new postgresql.conf
file. But during pg_createsubscriber, it will restart the standby
server using the default postgresql.conf file. And this might create
some issues.

Thanks and Regards,
Shlok Kyal