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

On Sun, Apr 9, 2017 at 4:22 AM, Michael Banck <michael(dot)banck(at)credativ(dot)de>
wrote:

> Hi,
>
> Am Freitag, den 24.03.2017, 19:32 +0100 schrieb Michael Banck:
> > On Thu, Mar 23, 2017 at 12:41:54PM +0100, Magnus Hagander wrote:
> > > On Tue, Mar 21, 2017 at 8:34 PM, Robert Haas <robertmhaas(at)gmail(dot)com>
> wrote:
> > > > So I tend to think that there should always be some explicit user
> > > > action to cause the creation of a slot, like --create-slot-if-needed
> > > > or --create-slot=name. That still won't prevent careless use of that
> > > > option but it's less dangerous than assuming that a user who refers
> to
> > > > a nonexistent slot intended to create it when, perhaps, they just
> > > > typo'd it.
> > >
> > > Well, the explicit user action would be "--slot". But sure, I can
> > > definitely live with a --create-if-not-exists.
> >
> > Can we just make that option create slot and don't worry if one exists
> > already? CreateReplicationSlot() can be told to not mind about already
> > existing slots, and I don't see a huge point in erroring out if the slot
> > exists already, unless somebody can show that this leads to data loss
> > somehow.
> >
> > > The important thing, to me, is that you can run it as a single
> > > command, which makes it a lot easier to work with. (And not like we
> > > currently have for pg_receivewal which requires a separate command to
> > > create the slot)
> >
> > Oh, that is how it works with pg_receivewal, I have to admit I've never
> > used it so was a bit confused about this when I read its code.
> >
> > So in that case I think we don't necessarily need to have the same user
> > interface at all. I first thought about just adding "-C, --create" (as
> > in "--create --slot=foo"), but this on second thought this looked a bit
> > shortsighted - who knows what flashy thing pg_basebackup might create in
> > 5 years... So I settled on --create-slot, which is only slightly more to
> > type (albeit repetive, "--create-slot --slot=foo"), but adding a short
> > option "-C" would be fine I thinkg "-C -S foo".
> >
> > So attached is a patch with adds that option. If people really think it
> > should be --create-slot-if-not-exists instead I can update the patch, of
> > course.
> >
> > I again added a second patch with some further refactoring which makes
> > it print a message on temporary slot creation in verbose mode.
>
> 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,

Jeff