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On 11/20/2013 10:06 AM, Soren Hansen wrote:
> 2013/11/18 Mike Spreitzer <mspreitz at us.ibm.com>:
>> There were some concerns expressed at the summit about scheduler
>> scalability in Nova, and a little recollection of Boris' proposal to
>> keep the needed state in memory.
>
>
>> I also heard one guy say that he thinks Nova does not really need a
>> general SQL database, that a NOSQL database with a bit of
>> denormalization and/or client-maintained secondary indices could
>> suffice.
>
> I may have said something along those lines. Just to clarify -- since
> you started this post by talking about scheduler scalability -- the main
> motivation for using a non-SQL backend isn't scheduler scalability, it's
> availability and resilience. I just don't accept the failure modes that
> MySQL (and derivatives such as Galera) impose.
>
>> Has that sort of thing been considered before?
>
> It's been talked about on and off since... well, probably since we
> started this project.
>
>> What is the community's level of interest in exploring that?
>
> The session on adding a backend using a non-SQL datastore was pretty
> well attended.

What about a hybrid solution?

There is data that is only used by the scheduler--for performance 
reasons maybe it would make sense to store that information in RAM as 
described at

https://blueprints.launchpad.net/nova/+spec/no-db-scheduler

For the rest of the data, perhaps it could be persisted using some 
alternate backend.

Chris