Re: [netconf] restconf collections

Andy Bierman <andy@yumaworks.com> Thu, 01 October 2020 16:17 UTC

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From: Andy Bierman <andy@yumaworks.com>
Date: Thu, 1 Oct 2020 09:17:01 -0700
Message-ID: <CABCOCHTBk52yyGH5Y2CrGcbV3FqEh8_c4od6LnXQdjT9rigKgg@mail.gmail.com>
To: =?UTF-8?Q?Martin_Bj=C3=B6rklund?= <mbj+ietf@4668.se>
Cc: Kent Watsen <kent+ietf@watsen.net>, Netconf <netconf@ietf.org>
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Subject: Re: [netconf] restconf collections
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On Thu, Oct 1, 2020 at 7:57 AM Martin Björklund <mbj+ietf@4668.se> wrote:

> Kent Watsen <kent+ietf@watsen.net> wrote:
> >
> >
> > > On Oct 1, 2020, at 9:23 AM, Martin Björklund <mbj+ietf@4668.se> wrote:
> > >
> > > Kent Watsen <kent+ietf@watsen.net> wrote:
> > >> Hi Qin,
> > >>
> > >>> Some opstate must be persisted, e.g., long-lived counters, logs,
> etc.,
> > >>> but it’s a good point about other opstate not being persisted.
> > >>> Perhaps “node-tags” can be used here, to differentiate which is
> > >>> which…and servers can indicate if/how they support the ephemeral
> > >>> opstate leafs in queries?
> > >>>
> > >>> [Qin]:That's a good case for node tag, in earlier discussion, we
> > >>> discussed operation type, which distinguishs cumulative statistics
> > >>> value from current value. The case discussed here is very close to
> > >>> operation type proposal discussed earlier.
> > >>
> > >> Yes.  Thank you for pointing that out.  I meant to make the same
> > >> observation before.  Indeed, such node-tags could have dual-purpose:
> > >> to guide a streaming-strategy and a querying-strategy for certain
> > >> nodes.
> > >>
> > >>
> > >>> Note sure how others feel about “direction: (c), but my primary
> > >>> use-case revolves around time-series data (e.g., logs), where the
> > >>> interest is commonly on the most-recent entries, so
> > >>> "reverse-->offset—>limit” works nicely.
> > >>>
> > >>> Perhaps an alternative would be to lift a concept from Python with
> > >>> negative indexes so, for instance, offset=-N and limit=-N gives the
> > >>> last N entries?
> > >>> [Qin]: Yes, that's what I thought as well, with negative indexes, (b)
> > >>> and (c) seems to me, can be combined.
> > >>
> > >> Can others comment on this?
> > >
> > > Isn't this just another syntax for the same function?
> >
> > No, it is not.
>
> How so?  Isn't the idea that you can first ask for offset=-10, then
> -20, etc, essentially walking the list backwards?  (I don't understand
> what a negative limit means though).
>
>


Can somebody explain the use-case for iterating a list backwards?
No customer has ever asked for this so I am wondering what we are all
missing.

I guess it isn't clear that offsets do not work for lists where entries
are added and/or deleted over time, unless lots of state is kept by the
server.
I guess if you are looking for the most expensive heavyweight solution
possible
then this is a good start.



>
> /martin
>

Andy


>
>
> >
> > K.
> >
> >
> > >
> > > /martin
> > >
> > >
> > >> Presumably, we could eliminate “direction” (c) with this approach.
> > >>
> > >> Without “direction”, I think that UIs can still support the ability to
> > >> do column-sorts, whereby the user clicks on a column’s header to
> > >> toggle ascending vs. descending presentation, but they’ll have to do
> > >> it client-side.
> > >>
> > >> That is, if wanting to see the 2nd page of results sorted by a column,
> > >> something like:
> > >>
> > >>    sort(column-name) --> offset(-2*pagesize) --> limit(pagesize)
> > >>
> > >> Followed by the client then flipping the results to present the
> > >> results in the user-selected order, right?
> > >>
> > >> That said, given that DB-backends that support sorts commonly also
> > >> support direction, it's unclear what this buys us.
> > >>
> > >>
> > >>>>> Sure, but I wonder if, e.g., a netmask filter, is supportable by
> > >>>>> common DB-backends.  I’m hoping we have some DB-experts on the
> list!
> > >>>>
> > >>>> See above.  It can be quite efficient even if the backend doesn't
> > >>>> support it.
> > >>>
> > >>> I don’t see that above, but I don’t doubt that it can be so, it’s
> just
> > >>> a whole lot of implementation complexity.  It seems that we
> > >>> should/must support servers doing it, we just need to find a way
> > >>> (node-tags?) to enable them to express that ability.
> > >>> [Qin]: My feeling is this efficiency more depends on the amount of
> > >>> data we need to request. If amount of data we request is huge, maybe,
> > >>> client-> server-> backend may be the better choice.
> > >>
> > >> Is it the amount of data requested or the number of entries in the
> > >> list?  At least, in my worldview, clients are always requesting a
> > >> “page” of data, so that part is rather consistently small.
> > >>
> > >> If the intention is to get a complete dump, then maybe the comment
> > >> from yesterday applies, whereby streaming to an external repository
> > >> that can be queried offline makes more sense?  - especially
> > >> considering that the number of on-box logs is likely to be only the
> > >> most recent (e.g., days), whereas the complete-dump type queries
> > >> likely wish to extend well-past that.
> > >>
> > >> K.
> > >>
> > >>
> >
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