[openstack-dev] [Ceilometer][Horizon] The future or pagination

Lyle, David david.lyle at hp.com
Wed Nov 13 17:51:09 UTC 2013

>From a purely UI perspective, the limit/offset is a lot more useful.  Then we can show links to previous page, next page and display the current page number.

Past mailing list conversations have indicated that limit/offset can be less efficient on the server side.  The marker/limit approach works for paginating UI side, just in a more primitive way.  With that approach, we are generally limited to a next page link only.


> -----Original Message-----
> From: John Dickinson [mailto:me at not.mn]
> Sent: Wednesday, November 13, 2013 10:09 AM
> To: OpenStack Development Mailing List (not for usage questions)
> Subject: Re: [openstack-dev] [Ceilometer][Horizon] The future or
> pagination
> Swift uses marker+limit for pagination when listing containers or objects
> (with additional support for prefix, delimiters, and end markers). This is
> done because the total size of the listing may be rather large, and going to a
> correct "page" based on an offset gets expensive and doesn't allow for
> repeatable queries.
> Pagination implies some sort of ordering, and I'm guessing
> (assuming+hoping) that your listings are based around something more
> meaningful that an incrementing id. By itself, "metric number 32592"
> doesn't mean anything, and listings like "go to metric 42000000 and give me
> the next 768 items" doesn't tell the consumer anything and probably isn't
> even a very repeatable query. Therefore, using a marker+prefix+limit style
> pagination system is very useful (eg "give me up to 1000 metrics that start
> with 'nova/instance_id/42/'"). Also, end_marker queries are very nice (half-
> closed ranges).
> One thing I would suggest (and I hope we change in Swift whenever we
> update the API version) is that you don't promise to return the full page in a
> response. Instead, you should return a "no matches" or "end of listing"
> token. This allows you the flexibility to return responses quickly without
> consuming too many resources on the server side. Clients can then continue
> to iterate over subsequent pages as they are needed.
> Something else that I'd like to see in Swift (it was almost added once) is the
> ability to reverse the order of the listings so you can iterate backwards over
> pages.
> --John
> On Nov 13, 2013, at 2:58 AM, Julien Danjou <julien at danjou.info> wrote:
> > Hi,
> >
> > We've been discussing and working for a while on support for
> > pagination on our API v2 in Ceilometer. There's a large amount that
> > already been done, but that is now stalled because we are not sure
> > about the consensus.
> >
> > There's mainly two approaches around pagination as far as I know, one
> > being using limit/offset and the other one being marker based. As of
> > today, we have no clue of which one we should pick, in the case we
> > would have a technical choice doable between these two.
> >
> > I've added the Horizon tag in the subject because I think it may
> > concern Horizon, since it shall be someday in the future one of the
> > main consumer of the Ceilometer API.
> >
> > I'd be also happy to learn what other projects do in this regard, and
> > what has been said and discussed during the summit.
> >
> > To a certain extend, we Ceilometer would also be happy to find common
> > technical ground on this to some extend so _maybe_ we can generalise
> > this into WSME itself for consumption from other projects.
> >
> > Cheers,
> > --
> > Julien Danjou
> > ;; Free Software hacker ; independent consultant ;;
> > http://julien.danjou.info
> > _______________________________________________
> > OpenStack-dev mailing list
> > OpenStack-dev at lists.openstack.org
> > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev

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