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> Neutron has protection against these now as of liberty with API level 
> retry
> operations so this shouldn't be a problem for neutron any more.

Jay Pipes wrote an awesome post about the problem itself and a solution 
earlier this year: 
http://www.joinfu.com/2015/01/understanding-reservations-concurrency-locking-in-nova/

Saying that though, we’re running the same setup as others have 
described - which is that we have a multi-writer mode Galera cluster 
with haproxy in front ensuring that only one node is actually written to 
- and it’s worked very well for us thus far.

—

-Nick

> On Dec 7, 2015 4:06 PM, "Matteo Panella" <matteo.panella at cnaf.infn.it>
> wrote:
>
>> On 2015-12-07 22:45, James Dempsey wrote:
>>
>>> +1 for designating one node as primary.  This helped us reduce some
>>> deadlocks that we were seeing when balancing sessions between DB 
>>> hosts.
>>>
>>
>> Keystone most likely won't be affected by writeset certification 
>> failures,
>> but other services (especially Neutron) are going to be hit by one 
>> sooner
>> or later.
>>
>> Unfortunately, Galera doesn't take very kindly "SELECT ... FOR 
>> UPDATE", so
>> you can't really do proper load balancing (aside from designating a
>> different node
>> as master in multiple listen stanzas, each one for a different set of
>> services).

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