On 08/13/2013 12:55 PM, Lyle, David (Cloud Services) wrote:
The marker/limit pagination scheme is inferior.
A bold statement that flies in the face of experience and the work
already done in all the other projects.
>The use of page/page_size allows access to arbitrary pages, whereas
limit/marker only allows forward progress.
I don't see this as a particularly compelling use case considering the
performance manifestations of using LIMIT OFFSET pagination.
>In Horizon's use case, with page/page_size we can provide the user
access to any page they have already visited, rather than just the
previous page (using prev/next links returned in the response).
I don't see this as a particularly useful thing, but in any case, you
could still do this by keeping the markers for previous pages on the
client (Horizon) side.
The point of marker/limit is to eliminate poor performance of LIMIT
OFFSET queries and to force proper index usage in the listing queries.
You can see the original discussion about this from more than two years
and even see where I was originally arguing for a LIMIT OFFSET strategy
and was brought around to the current limit/marker strategy by the
responses of Justin Santa Barbara and Greg Holt:
https://lists.launchpad.net/openstack/msg02548.html
Best,
-jay
-David
On 08/13/2013 10:29 AM, Pipes, Jay wrote:
On 08/13/2013 03:05 AM, Yee, Guang wrote:
Passing the query parameters, whatever they are, into the driver if
the given driver supports pagination and allowing the driver to
override the manager default pagination functionality seem reasonable to me.
Please do use the standards that are supported in other OpenStack services
already: limit, marker, sort_key and sort_dir.
Pagination is meaningless without a sort key and direction, so picking a sensible
default for user/project records is good. I'd go with either created_at (what
Glance/Nova/Cinder use..) or with the user/project >UUID.
The Glance DB API pagination is well-documented and clean [1]. I highly
recommend it as a starting point.
Nova uses the same marker/limit/sort_key/sort_dir options for queries that it
allows pagination on. An example is the
instance_get_all_by_filters() call [2].
Cinder uses the same marker/limit/sort_key/sort_dir options for query
pagination as well. [3]
Finally, I'd consider supporting the standard change-since parameter for listing operations.
Both Nova [4] and Glance [5] support the parameter, which is useful for tools that poll the
APIs for "new" >events/records.
In short, go with what is already a standard in the other projects...
Best,
-jay
[1]
https://github.com/openstack/glance/blob/master/glance/db/sqlalchemy/api.py#L429
[2]
https://github.com/openstack/nova/blob/master/nova/db/sqlalchemy/api.py#L1709
[3]
https://github.com/openstack/cinder/blob/master/cinder/common/sqlalchemyutils.py#L33
[4]
https://github.com/openstack/nova/blob/master/nova/db/sqlalchemy/api.py#L1766
[5]
https://github.com/openstack/glance/blob/master/glance/db/sqlalchemy/api.py#L618
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