Why is unit id mandatory in config-changed context?

[Andreas Hasenack]

On Fri, May 31, 2013 at 8:42 PM, Gustavo Niemeyer <gustavo at niemeyer.net>wrote:

> On Fri, May 31, 2013 at 8:14 PM, Andreas Hasenack <andreas at canonical.com>
> wrote:
> > But aren't the key-value pairs that I set in the relation the same for
> all
> > units?
>
> Yes, because it is associated with the local unit. It's similar to the
> following scheme:
>
> relation R1:
>     unit U1:
>           setting S1=V1
>           setting S2=V2
>     unit U2:
>           setting S1=V3
>           setting S2=V4
>           setting S3=V5
>     unit U3:
>           setting S1=V6
>
> If U1 does relation-set S1=V1, it sets its own S1 setting to V1. If it
>

I think I have a basic misunderstanding of "scope". I didn't know the
relation "variables" (let me call S1..S3 that) could be local and specific
to a unit. I thought all changes would eventually be propagated to all
units, meaning these "variables" are "global" in the relation. Let's take
your example above:

U1 does relation-set S1=V1 in a hook relation, for example. When this hook
finishes successfully, this change (S1=V1) is committed and the
relation-changed hook is fired in U2 and U3, right?

If U2 or U3 do relation-get S1 without specifying a unit, they will get V1
I suppose. But what if U2 does "relation-get -r R1 S1 U3"? Will it get V6
or V1? "Depends"?
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