Alexander:
To help me understand your proposal, let us move to the previous example:
Previous example:
list foo {
key id;
leaf id { type int32; }
leaf a { type int32; }
}
local config:
foo 42
In ephemeral config we now do SET /foo[id=42]/a to 4711. Thus, in
ephemeral we now have a single node (a) with value 4711.
Your model:
a) The value 4711 - would be a "non-golden" copy.
b) It would not be written through to the the "golden copy".
Questions:
a) How would you specify a "write-through" copy?
b) Can I2RS decide later it wants to write-through the golden copy? Or are
variables only "non-write-through" and "write-through"?
c) If we delete foo 42, what happens?
Thank you,
Sue Hares
From: i2rs [mailto:[email protected]] On Behalf Of Alexander Clemm
(alex)
Sent: Thursday, September 25, 2014 8:57 PM
To: Andy Bierman; Martin Bjorklund
Cc: Jeffrey Haas; [email protected]; Eric Voit (evoit)
Subject: Re: [i2rs] Two thoughts on an ephemeral data store
FWIW, I would think the semantics should be kept simple.
The complexity here comes from the fact that there are dependencies between
different data stores, and some objects that are part of one data store need
to be reflected in a different data store.
It would seem this can be addressed with two fairly simple principles:
(a) A datastore needs to have a clear way to reference objects in a
different datastore, really have them incorporated into the same namespace.
(b) It needs to be clear who owns the "golden copy" of an object. I needs
to be clear which objects are "authoritatively owned" by a datastore vs
which ones are reference. This is the datastore where the object is
maintained, updated, created; this is where conditions and constraints are
evaluated, etc.
Where an ephemeral datastore has dependencies on data in another datastore,
it should incorporate these other objects "by reference". The objects that
are authoritatively owned by the ephemeral datastore can refer to those
objects, have them referred to in conditions and constraints, and so on.
(This can also indicate which ephemeral objects are to be removed when an
object in the other datastore they depend on is deleted, etc)
Changes to the non-ephemeral objects (e.g. the running datastore) have to be
made to the "golden copy", i.e. the owning datastore. One way to do that
involves implementing a "write-through" operation, in which an update to an
ephemeral copy of the object is realized by having the server of the
ephemeral datastore turn around and make a corresponding request at the
other datastore.
Very simple semantics. I think this is preferrable to have different copies
of the same object in different datastores, requiring "logical anding" (or
other inter-datastore arithmetic) of different copies representing the same
object to figure out what actual value is in effect, etc.
In the netmod WG, we have today posted a draft for what we refer to as
requirements for a peer mount
(http://www.ietf.org/internet-drafts/draft-voit-netmod-peer-mount-requiremen
ts-00.txt), motivating why a it would be useful to have a capability to
"mount" subtrees from a remote datastore into a local datastore, and the
requirements that such a capability needs to address. While the original
use case and motivation described there are somewhat different, it seems
applicable to the discussion here.
--- Alex
From: i2rs [mailto:[email protected]] On Behalf Of Andy Bierman
Sent: Thursday, September 25, 2014 8:44 AM
To: Martin Bjorklund
Cc: Jeffrey Haas; [email protected]
Subject: Re: [i2rs] Two thoughts on an ephemeral data store
On Thu, Sep 25, 2014 at 7:39 AM, Martin Bjorklund <[email protected]> wrote:
Jeffrey Haas <[email protected]> wrote:
> On Thu, Sep 25, 2014 at 12:29:35PM +0200, Martin Bjorklund wrote:
> > Jeffrey Haas <[email protected]> wrote:
> > > In the proposed overlay model, presume that we have ephemeral data
from a
> > > model that lives within an augmentation to a local config model. In
other
> > > words, the ephemeral nodes are children of the local config nodes.
> > >
> > > Presume, per discussion, that the local config lives in the "config"
data
> > > store and that the ephemeral config - the augmenting nodes above -
live in
> > > the ephemeral data store.
> > >
> > > If we delete the container in the local config that the epehemeral
config is
> > > augmenting, is there any expectation that such a deletion should carry
> > > through to the ephemeral config?
> > >
> > > Per the netmod interim discussion, probably not.
> >
> > My interpretation of the interim discussion is that the deletion
> > carries through.
>
> To be clear what I meant, consider:
>
> local config: ephemeral:
> A A/B - B is introduced as an augmentation of A
I think there might be a terminology confusion here, so let's do a
simple example.
list foo {
key id;
leaf id { type int32; }
leaf a { type int32; }
}
local config:
foo 42
In ephemeral config we now do SET /foo[id=42]/a to 4711. Thus, in
ephemeral we now have a single node (a) with value 4711.
What happens if we in local config delete foo 42?
If /foo[id=42]/a is NOT deleted from the ephemeral config, what is now
presented to the internal apps?
Yes -- and what is presented to a client that retrieves the ephemeral config
in a GET request? IMO, coupling the datastores does not make sense.
Your example is 1 reason I prefer the "shadow shapshot" approach.
I think the local config and client that added the "foo" entry in the
ephemeral datastore
are meant to have different priorities. The entries are not coupled.
One wins and the other loses (main use-case is that ephemeral wins).
Editing "foo 42" in the local config just changes what will be installed as
local config
when the device restarts (or the ephemeral state is removed). It should not
change
the injected I2RS state at all. IMO it is really important that edits stay
within a single
datastore.
/martin
Andy
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