[rabbitmq-discuss] |Spam| Re: Queue message replication in clusters with mirrored queues

[Devangana Tarafdar]

Hello,

Thanks for the prompt reply !

For point 2, I understand your answer. My phrasing of the question was
incorrect. I suppose my question is more about the messages that are routed
to the queue.  Would other nodes in a cluster hold a copy of the message ?

Thank you for the reply,

Devangana


On Mon, May 19, 2014 at 10:18 AM, Simon MacMullen <simon at rabbitmq.com>wrote:

> On 19/05/2014 15:43, Devangana Tarafdar wrote:
>
>> I am trying to understand how clusters with mirrored queues operate on
>> data (messages as well as data about queues). From the doc at
>> https://www.rabbitmq.com/ha.html
>>
>> "All actions other than publishes go only to the master, and the master
>> then broadcasts the effect of the actions to the slaves. Thus clients
>> consuming from a mirrored queue are in fact consuming from the master."
>> So I understand that;
>>
>> 1.  There is only one node that has the queue process running. Other
>> nodes have enough information to start up a queue process should the
>> master go down.
>>
>
> Other nodes have a slave process that is quite a lot of the way towards
> being a queue, it maintains (almost) all the same data structures, it just
> never talks to clients.
>
> So it depends how you look at it.
>
>  2. Queue data for persistent queues is stored on disk on all nodes of
>> cluster. So persistent data is replicated.
>> 3. Queue data that is not persistent is stored on ram on all nodes of
>> the cluster. So ram data is replicated.
>>
>
> Replication is orthogonal to persistence really. And it doesn't really
> make sense to think of queues as "persistent" or not since durable queues
> can contain transient messages, and transient queues can page to disk under
> memory pressure...
>
> Cheers, Simon
>
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