Re: speed up a logical replica setup

On Sat, Mar 16, 2024 at 9:13 PM Euler Taveira <euler(at)eulerto(dot)com> wrote:
>
> On Fri, Mar 15, 2024, at 3:34 AM, Amit Kapila wrote:
>
> Did you consider adding options for publication/subscription/slot
> names as mentioned in my previous email? As discussed in a few emails
> above, it would be quite confusing for users to identify the logical
> replication objects once the standby is converted to subscriber.
>
>
> Yes. I was wondering to implement after v1 is pushed. I started to write a code
> for it but I wasn't sure about the UI. The best approach I came up with was
> multiple options in the same order. (I don't provide short options to avoid
> possible portability issues with the order.) It means if I have 3 databases and
> the following command-line:
>
> pg_createsubscriber ... --database pg1 --database pg2 --database3 --publication
> pubx --publication puby --publication pubz
>
> pubx, puby and pubz are created in the database pg1, pg2, and pg3 respectively.
>

With this syntax, you want to give the user the option to specify
publication/subscription/slot name for each database? If so, won't it
be too much verbose?

> It seems we care only for publications created on the primary. Isn't
> it possible that some of the publications have been replicated to
> standby by that time, for example, in case failure happens after
> creating a few publications? IIUC, we don't care for standby cleanup
> after failure because it can't be used for streaming replication
> anymore. So, the only choice the user has is to recreate the standby
> and start the pg_createsubscriber again. This sounds questionable to
> me as to whether users would like this behavior. Does anyone else have
> an opinion on this point?
>
>
> If it happens after creating a publication and before promotion, the cleanup
> routine will drop the publications on primary and it will eventually be applied
> to the standby via replication later.
>

Do you mean to say that the next time if user uses
pg_createsubscriber, it will be ensured that all the prior WAL will be
replicated? I think we need to ensure that after the restart of this
tool and before it attempts to create the publications again, the WAL
of the previous drop has to be replayed.

--
With Regards,
Amit Kapila.