Re: pg_basebackup and replication slots

On 29 July 2015 at 11:43, Andres Freund <andres(at)anarazel(dot)de> wrote:

> On 2015-07-29 09:17:04 +0100, Simon Riggs wrote:
> > On 29 July 2015 at 09:09, Andres Freund <andres(at)anarazel(dot)de> wrote:
> > > The point of using a temporary slot is to not have a
> > > leftover slot afterwards, reserving resources. Especially important if
> > > the basebackup actually failed...
> > >
> >
> > Creating a slot and then deleting it if the session disconnects does not
> > successfully provide the functionality desired above.
>
> Uh? If you create the slot, start streaming, and then start the
> basebackup, it does. It does *not* guarantee that the base backup can be
> converted into a replica, but it's sufficient to guarantee it can
> brought out of recovery.
>

Perhaps we are misunderstanding the word "it" here. "it can be brought out
of recovery"?

You appear to be saying that a backup that disconnects before completion is
useful in some way. How so?

If the slot is cleaned up on disconnect, as suggested, then you end up with
half a backup and WAL is cleaned up. The only possible use for slots is to
reserve resources (as you say); the resources will clearly not be reserved
if we drop the slot on disconnect. What use is that?

--
Simon Riggs http://www.2ndQuadrant.com/
<http://www.2ndquadrant.com/>
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