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Hello,

Thank you for bringing that up.
I was thinking (but it seems I was wrong) that the fanout/reply queues
were used for a one shot message/reply.

Besides that, I am also wondering how much cpu power we will need to
replicate such queues?

I guess I can can do the math from what we are currently running in
production :)

Have you tried on a big cluster on your side?

Cheers,

Arnaud


On 02.09.22 - 08:19, Felix Hüttner wrote:
> Hi everyone,
> 
> the largescale-sig currently recommends the following rabbitmq policy [1]: '^(?!(amq\.)|(.*_fanout_)|(reply_)).*'.
> 
> If I found the history of this setting correctly, it resulted from this mailinglist thread [2] which came to the conclusion:
> 
> > * use durable-queue and replication for long-running queues/exchanges
> > * use non-durable-queue without replication for short (fanout, reply_) queues
> 
> However I am unsure if reply_ queues are actually shorted lived than the "long-running" ones.
> If we take the example of the cinder-scheduler we have the following queues:
> 
> * cinder-scheduler: Tied to the lifetime of the whole cinder-scheduler cluster; currently durable + replicated
> * cinder-scheduler.myhostname: Tied to the lifetime of the cinder-scheduler service, but not removed when the service stops; currently durable + replicated
> * cinder-scheduler_fanout_somerandomid: Tied to the lifetime of the cinder-scheduler service, but removed when the service stops; currently neither durable nor replicated
> * reply_somerandomid: Tied to the lifetime of the cinder-scheduler service, but removed when the service stops; currently neither durable nor replicated
> 
> If I read got all of the above correctly then reply_ and fanout queues are actually not shorter lived than the normal queue to send requests to that service.
> The only difference is that we remove them when the service itself stops.
> 
> Therefor I want to propose the question if we should not also make these queues durable and replicated.
> 
> Thank you
> 
> [1]: https://docs.openstack.org/large-scale/other/rabbitmq.html#pattern
> [2]: https://lists.openstack.org/pipermail/openstack-discuss/2020-August/016562.html
> 
> --
> Felix Huettner
> 
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