[Openstack] A single cross-zone database?
andrew at cloudscaling.com
Wed Mar 16 18:14:02 UTC 2011
Global temporal consistency is a myth.
If you decide not to cache and support pagination then querying every zone
for every page is potentially as misleading as caching because what should
be on each page could change for every request.
+1 for cache with ttl
On Wed, Mar 16, 2011 at 11:58 AM, Paul Voccio <paul.voccio at rackspace.com>wrote:
> I would agree. The caching would go with the design tenet #7: Accept
> eventual consistency and use it where it is appropriate.
> If we're ok with accepting that the list may or may not always be up to
> date and feel its appropriate, we should be good with the caching.
> On 3/16/11 11:45 AM, "Ed Leafe" <ed.leafe at rackspace.com> wrote:
> >On Mar 16, 2011, at 12:23 PM, Paul Voccio wrote:
> >> Not only is this expensive, but there is no way I can see at the moment
> >>to do pagination, which is what makes this really expensive. If someone
> >>asked for an entire list of all their instances and it was > 10,000 then
> >>I would think they're ok with waiting while that response is gathered
> >>and returned. However, since the API spec says we should be able to do
> >>pagination, this is where asking each zone for all its children every
> >>time gets untenable.
> > This gets us into the caching issues that were discussed at the last
> >summit. We could run the query and then cache the results at the
> >endpoint, but this would require accepting some level of staleness of the
> >results. The cache would handle the paging, and some sort of TTL would
> >have to be established as a balance between performance and staleness.
> >-- Ed Leafe
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