Open Stack

On 05/14/2014 02:49 PM, Сергей Мотовиловец wrote:
> Hello everyone!

Hi Motovilovets :) Comments and questions for you inline...

> I'm facing some troubles with nova and cinder here.
>
> I have 2 control nodes (active/active) in my testing environment with
> Percona XtraDB cluster (Galera+xtrabackup) + garbd on a separate node
> (to avoid split-brain) Â + OpenStack Icehouse, latest from Ubuntu 14.04
> main repo.
>
> The problem is horizontal scalability of nova-conductor and
> cinder-scheduler services, seems like all active instances of these
> services are trying to execute same MySQL queries they get from
> Rabbit, which leads to numerous deadlocks in set-up with Galera.Â

Are you using RabbitMQ in clustered mode? Also, how are you doing your 
load balancing? Do you use HAProxy or some appliance? Do you have sticky 
sessions enabled for your load balancing?

> In case when multiple nova-conductor services are running (and using
> MySQL instances on corresponding control nodes) it appears as "Deadlock
> found when trying to get lock; try restarting transaction" in log.
> With cinder-scheduler it leads to "InvalidBDM: Block Device Mapping is
> Invalid."

So, it's not actually a deadlock that is occurring... unless I'm 
mistaken (I've asked a Percona engineer to take a look at this thread to 
double-check me), the error about "Deadlock found..." is actually *not* 
a deadlock. It's just that Galera uses the same InnoDB error code as a 
normal deadlock to indicate that the WSREP certification process has 
timed out between the cluster nodes. Would you mind pastebin'ing your 
wsrep.cnf and my.cnf files for us to take a look at? I presume that you 
do not have much latency between the cluster nodes (i.e. they are not 
over a WAN)... let me know if that is not the case.

It would also be helpful to see your rabbit and load balancer configs if 
you can pastebin those, too.

> Is there any possible way to make multiple instances of these services
> running simultaneously and not duplicating queries?Â

Yes, it most certainly is. At AT&T, we ran Galera clusters of much 
bigger size with absolutely no problems due to this cert timeout problem 
that manifests itself as a deadlock, so I know it's definitely possible 
to have a clean, performant, multi-writer Galera solution for OpenStack. :)

Best,
-jay

> (I don't really like the idea of handling this with Heartbeat+Pacemaker
> or other similar stuff, mostly because I'm thinking about equal load
> distribution across control nodes, but in this case it seems like it has
> an opposite effect, multiplying load on MySQL)
>
> Another thing that is extremely annoying: if instance stuck in ERROR
> state because of deadlock during its termination - it is impossible to
> terminate instance anymore in Horizon, only via nova-api with
> reset-state. How can this be handled?
>
> I'd really appreciate any help/advises/thoughts regarding these problems.
>
>
> Best regards,
> Motovilovets Sergey
> Software Operation Engineer
>
>
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