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On 07/22/2013 12:51 PM, John Garbutt wrote:
> On 22 July 2013 13:23, Boris Pavlovic <boris at pavlovic.me> wrote:
>> I see only one race condition. (in current solution we have the same
>> situtaiton)
>> Between request to compute node and data is updated in DB, we could use
>> wrong state of compute node.
>> By the way it is fixed by retry.
> 
> This race turns out to be a big deal when there are bursts of VM.start requests.
> 
> I am currently thinking about ways we can look to eliminate this one.
> Hoping to have a design summit session on that.

Cool.  In addition to retries, it's somewhat mitigated by using the
scheduler_host_subset_size to reduce the chance that multiple schedulers
choose the same host.

# New instances will be scheduled on a host chosen randomly
# from a subset of the N best hosts. This property defines the
# subset size that a host is chosen from. A value of 1 chooses
# the first host returned by the weighing functions. This
# value must be at least 1. Any value less than 1 will be
# ignored, and 1 will be used instead (integer value)
#scheduler_host_subset_size=1

-- 
Russell Bryant