[openstack-dev] [keystone] Pagination
yufang521247 at gmail.com
Wed Aug 14 16:01:01 UTC 2013
2013/8/14 Kieran Spear <kispear at gmail.com>
> On 14/08/2013, at 7:40 AM, Jay Pipes <jaypipes at gmail.com> wrote:
> > On 08/13/2013 05:04 PM, Gabriel Hurley wrote:
> >> I have been one of the earliest, loudest, and most consistent PITA's
> about pagination, so I probably oughta speak up. I would like to state
> three facts:
> >> 1. Marker + limit (e.g. forward-only) pagination is horrific for
> building a user interface.
> >> 2. Pagination doesn't scale.
> >> 3. OpenStack's APIs have historically had useless filtering
> >> In a world where pagination is a "must-have" feature we need to have
> page number + limit pagination in order to build a reasonable UI.
> Ironically though, I'm in favor of ditching pagination altogether. It's the
> lowest-common denominator, used because we as a community haven't buckled
> down and built meaningful ways for our users to get to the data they really
> >> Filtering is great, but it's only 1/3 of the solution. Let me break it
> down with problems and high level "solutions":
> >> Problem 1: I know what I want and I need to find it.
> >> Solution: filtering/search systems.
> > This is a good place to start. Glance has excellent filtering/search
> capabilities -- built in to the API from early on in the Essex timeframe,
> and only expanded over the last few releases.
> > Pagination solutions should build on a solid filtering/search
> functionality in the API, where there is a consistent sort key and
> direction (either hard-coded or user-determined, doesn't matter).
> > Limit/offset pagination solutions (forward and backwards paging, random
> skip-to-a-page) are inefficient from a SQL query perspective and should be
> a last resort, IMO, compared to limit/marker. With some smart
> session-storage of a page's markers, backwards paging with limit/marker
> APIs is certainly possible -- just store the previous page's marker.
> Not just the previous page's marker, but the marker of every previous page
> since we would like to be able to click the previous button more than once.
> Any previous markers we store are also likely to become stale pretty
> quickly. And all this is based on the assumption that the user's session
> even started at the first 'page' - it could be they followed a link from
> elsewhere in Horizon or the greater internet.
> I think we don't have to store previous pages' markers. Just storing
current page's markers is OK. Nova or Glance has supported 'sort_dir' for
long, if you want to go to the previous page, just use the first entry of
current page as marker and set sort_dir as 'asc'; Otherwise, use the last
entry of current page as marker and set sort_dir as ‘desc’.
> I completely agree with Dolph that this is something the client shouldn't
> need to care about at all. The next/prev links returned with each page of
> results should hide all of this. next/prev links also make it trivial for
> the client to discover whether there's even a next page at all, since we
> don't want to make a user click a link to go to an empty page.
> Having said that, I think we can improve the current marker/limit system
> without hurting performance if we split the marker into 'before' and
> 'after' parameters. That way all the information needed to go forward or
> backwards is included in the results for the current page. Supporting
> 'before' should be as simple as reversing the sort order and then flipping
> the order of the results.
> >> Problem 2: I don't know what I want, and it may or may not exist.
> >> Solution: tailored discovery mechanisms.
> > This should not be a use case that we spend much time on. Frankly, this
> use case can be summarized as "the window shopper scenario". Providing a
> quality search/filtering mechanism, including the *API* itself providing
> REST-ful discovery of the filters and search criteria the API supports, is
> way more important...
> >> Problem 3: I need to know something about *all* the data in my system.
> >> Solution: reporting systems.
> > Sure, no disagreement there.
> >> We've got the better part of none of that.
> > I disagree. Some of the APIs have support for a good bit of
> search/filtering. We just need to bring all the projects up to search
> speed, Captain.
> > Best,
> > -jay
> > p.s. I very often go to the second and third pages of Google searches.
> :) But I never skip to the 127th page of results.
> > > But I'd like to solve these issues. I have lots of thoughts on all of
> those, and I think the UX and design communities can offer a lot in terms
> of the usability of the solutions we come up with. Even more, I think this
> would be an awesome working group session at the next summit to talk about
> nothing other than "how can we get rid of pagination?"
> >> As a parting thought, what percentage of the time do you click to the
> second page of results in Google?
> >> All the best,
> >> - Gabriel
> >> _______________________________________________
> >> OpenStack-dev mailing list
> >> OpenStack-dev at lists.openstack.org
> >> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
> > _______________________________________________
> > OpenStack-dev mailing list
> > OpenStack-dev at lists.openstack.org
> > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
> OpenStack-dev mailing list
> OpenStack-dev at lists.openstack.org
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the OpenStack-dev