Open Stack

2016-07-27 2:20 GMT+03:00 Sam Morrison <sorrison at gmail.com>:

>
> On 27 Jul 2016, at 4:05 AM, Dmitry Mescheryakov <
> dmescheryakov at mirantis.com> wrote:
>
>
>
> 2016-07-26 2:15 GMT+03:00 Sam Morrison <sorrison at gmail.com>:
>
>> The queue TTL happens on reply queues and fanout queues. I don’t think it
>> should happen on fanout queues. They should auto delete. I can understand
>> the reason for having them on reply queues though so maybe that would be a
>> way to forward?
>>
>> Or am I missing something and it is needed on fanout queues too?
>>
>
> I would say we do need fanout queues to expire for the very same reason we
> want reply queues to expire instead of auto delete. In case of broken
> connection, the expiration provides client time to reconnect and continue
> consuming from the queue. In case of auto-delete queues, it was a frequent
> case that RabbitMQ deleted the queue before client reconnects ... along
> with all non-consumed messages in it.
>
>
> But in the case of fanout queues, if there is a broken connection can’t
> the service just recreate the queue if it doesn’t exist? I guess that means
> it needs to store the state of what the queue name is though?
>
> Yes they could loose messages directed at them but all the services I know
> that consume on fanout queues have a re sync functionality for this very
> case.
>
> If the connection is broken will oslo messaging know how to connect to the
> same queue again anyway? I would’ve thought it would handle the disconnect
> and then reconnect, either with the same queue name or a new queue all
> together?
>

oslo.messaging handles reconnect perfectly - on connect it just
unconditionally declares the queue and starts consuming from it. If queue
already existed, the declaration operation will just be ignored by RabbitMQ.

For your earlier point that services re sync and hence messages lost in
fanout are not that important, I can't comment on that. But after some
thinking I do agree that having big expiration time for fanouts is
non-adequate for big deployments anyway. How about we split
rabbit_transient_queues_ttl
into two parameters - one for reply queue and one for fanout ones? In that
case people concerned with messages piling up in fanouts might set it to 1,
which will virtually make these queues behave like auto-delete ones (though
I strongly recommend to leave it at least at 20 seconds, to give service a
chance to reconnect).

Thanks,

Dmitry



>
> Sam
>
>
>
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