Open Stack

IMHO, I don't actually think supporting both would be confusing to the user, unless the user
tried to supply both and we didn't just return an error saying "Nope, only use one or the other".
 As for the use case presented, while I personally have never needed it with OpenStack (I've never actually
had that many resources, probably since I'm a developer and not a deployer), I've definitely
used a similar workflow with other applications which supported pagination via offset.  I definitely
think it could be a useful feature.

Best Regards,
Solly Ross

----- Original Message -----
From: "Jay Pipes" <jaypipes at gmail.com>
To: openstack-dev at lists.openstack.org
Sent: Tuesday, March 18, 2014 3:30:06 PM
Subject: Re: [openstack-dev] Offset support in REST API pagination

On Tue, 2014-03-18 at 13:30 -0500, Steven Kaufer wrote:
> Jay Pipes <jaypipes at gmail.com> wrote on 03/18/2014 12:02:50 PM:
> 
> > From: Jay Pipes <jaypipes at gmail.com>
> > To: openstack-dev at lists.openstack.org, 
> > Date: 03/18/2014 12:15 PM
> > Subject: Re: [openstack-dev] Offset support in REST API pagination
> > 
> > On Tue, 2014-03-18 at 11:31 -0500, Steven Kaufer wrote:
> > > First, here is some background on this topic:
> > >  http://www.gossamer-threads.com/lists/openstack/dev/2777
> > > 
> > > Does anyone have any insight as to why offset is not supported in
> the
> > > REST API calls that support pagination?   I realize that there are
> > > tradeoffs when using a offset (vs. marker) but I believe that
> there is
> > > value in supporting both.  For example, if you want to jump to the
> > > n-th page of data without having to traverse all of the previous
> > > pages.
> > > 
> > > Is there a reason why the APIs do not support either a marker or
> an
> > > offset (obviously not both) on the API request?  It appears that
> > > sqlalchemy has offset support.
> > > 
> > > Also, it seems that cinder at least looks for the offset parameter
> > > (but ignores it).  Does this mean that it was supported at one
> time
> > > but later the support was removed?
> > >  https://github.com/openstack/cinder/blob/master/cinder/api/v2/
> > volumes.py#L214
> > > 
> > > Thanks for the information.
> > 
> > Hail to thee, stranger! Thou hast apparently not passed into the
> cave of
> > marker/offset before!
> > 
> > I humbly direct you to buried mailing list treasures which shall
> > enlighten you!
> > 
> > This lengthy thread shall show you how yours truly was defeated in
> > written combat by the great Justin Santa Barbara, who doth exposed
> the
> > perils of the offset:
> > 
> > http://www.gossamer-threads.com/lists/openstack/dev/2803
> > 
> > A most recent incantation of the marker/offset wars is giveth here:
> > 
> >
> http://lists.openstack.org/pipermail/openstack-dev/2013-November/018861.html
> > 
> > Best of days to you,
> > -jay
> 
> Jay:
> 
> Thanks for the feedback and the history on this topic. 

No probs. Thanks for indulging my Renaissance binge this morning.

> I understand that the limit/marker
> approach is superior when simply traversing all of the pages. However,
> consider the
> following:
> 
> - User knows that there are 1000 items (VMs, volumes, images, really
> doesn't matter)
> - User knows that the item that they want is in roughly the middle of
> the data set (assume
> everything is sorted by display name)
> - User cannot remember the exact name so a filter will not help and
> changing the sort 
> direction will not help (since the item they want it is in the middle
> of the dataset)
> - User supplies an offset of 500 to jump into the middle of the data
> set
> - User then uses the marker approach to traverse the pages from this
> point to find the
> item that they want
> 
> In this case the offset approach is not used to traverse pages so
> there are no issues with
> missing an item or seeing a duplicate.

I guess I wonder how common that use case is, actually. I can't remember
ever running into a user who asked for such a thing, but perhaps that's
just me.

> Why couldn't the APIs support either marker or offset on a given
> request? 

I think for two reasons:

1) Would be potentially quite confusing to the user
2) We're lazy? :)

> Also, to encourage
> the use of marker instead of offset, the next/previous links on any
> request with an offset
> supplied should contain the appropriate marker key values -- this
> should help discourage
> simply increasing the offset when traversing the pages.

Well, yes, this already happens today in the projects that support
pagination, AFAIK.

Best,
-jay

> I realize that if only one solution had to be chosen, then
> limit/marker would always win
> this war. But why can't both be supported?
> 
> Thanks,
> 
> Steven Kaufer
> 
> > 
> > 
> > _______________________________________________
> > 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



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