Re: speed up a logical replica setup

On Mon, Mar 18, 2024 at 9:37 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> 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.
>

On further thinking, the WAL for such dropped publications should get
replayed eventually before the WAL for new publications (the
publications which will be created after restart) unless the required
WAL is removed on primary due to some reason.

--
With Regards,
Amit Kapila.