[openstack-dev] [keystone] Pagination

Jay Pipes jaypipes at gmail.com
Tue Aug 13 21:40:08 UTC 2013

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 capabilities.
> 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 want.
> 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.

> 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.


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
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