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Re: Multi-Cluster/Zone - Devil in the Details ...


Good points Soren, and this is why I was suggesting we not solve this
problem with a cache, but instead an eventually consistent replication
stream of the aggregate data.


On Wed, Feb 16, 2011 at 11:12:50PM +0100, Soren Hansen wrote:
> 2011/2/16 Ed Leafe <ed@xxxxxxxxx>:
> > This was one of the issues we discussed during the sprint planning. I believe (check with cyn) that the consensus was to use a caching strategy akin to DNS: e.g., if zone A got a request for instance ID=12345, it would check to see if it had id 12345 in its cache. If not, it would ask all of its child nodes if they knew about that instance. That would repeat until the instance was found, at which point every upstream server would now know about where to reach 12345.
> Has any formal analysis been done as to how this would scale?
> I have a couple of problems with this approach:
>  * Whenever I ask something for information and I get out-of-date,
> cached data back I feel like I'm back in 2003. And 2003 sucked, I
> might add.
>  * Doesn't this caching strategy only help if people are asking for
> the same stuff over and over? It doesn't sound very awesome if 100
> requests for new stuff coming in at roughly the same time causes a
> request to be sent to every single compute node (or whereever the data
> actually resides). I'm assuming breadth-first search here, of course.
> -- 
> Soren Hansen
> Ubuntu Developer    http://www.ubuntu.com/
> OpenStack Developer http://www.openstack.org/
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