Re: Create replication slot in pg_basebackup if requested and not yet present

Hi,

Am Mittwoch, den 06.09.2017, 12:22 -0400 schrieb Peter Eisentraut:
> On 8/18/17 05:28, Michael Banck wrote:
> > > > Rebased, squashed and slighly edited version attached. I've added this
> > > > to the 2017-07 commitfest now as well:
> > > >
> > > > https://commitfest.postgresql.org/14/1112/
> > >
> > > Can you rebase this past some conflicting changes?
> >
> > Thanks for letting me know, PFA a rebased version.
>
> I have reviewed the thread so far. I think there is general agreement
> that something like this would be good to have.
>
> I have not found any explanation, however, why the "if not exists"
> behavior is desirable, let alone as the default. I can only think of
> two workflows here: Either you have scripts for previous PG versions
> that create the slot externally, in which can you omit --create, or you
> use the new functionality to have pg_basebackup create the slot. I
> don't see any use for pg_basebackup to opportunistically use a slot if
> it happens to exist. Even if there is one, it should not be the
> default. So please change that.

Ok, I tried to research why that was the case and couldn't find any
trace of a discussion either.

So we should just error out in CreateReplicationSlot() in case a slot
exists, right? I think having yet another option like --create-if-not-
exists does not sound needed from what you wrote above.

> A minor point, I suggest to print the message about the replication slot
> being created *after* the slot has been created. This aligns with how
> logical replication subscriptions work.

Ok.

> I don't see the need for printing a message about temporary slots.
> Since they are temporary, they will go away automatically, so there is
> nothing the user needs to know there.

Ok. I thought I'd remembered some request around having this reported
always (maybe from Magnus), but I couldn't find anything in the prior
discussions either.

If we don't print the message for temporary slots, then the
CreateReplicationSlot() refactoring and the addition of the
temp_replication_slot argument would be no longer needed, or is this
something useful on its own?

Thanks,

Michael

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