[rabbitmq-discuss] Ordering of messages after txRollback()

Sun Jun 6 19:13:09 BST 2010

The only thing a rollback on the consuming side can do is *undo acks*,  
and there's no difference between never acking and rolling back acks  
as far as the broker is concerned. I'm just mentioning that since - if  
I'm understanding correctly - it is a valid if limited use for TXs on  
the consumer side.

Sent from my iPhone

On Jun 6, 2010, at 2:05 PM, "Oleg Zhurakousky"  
<ozhurakousky at vmware.com> wrote:

> Thanks Matthew
>
> Let me get this straight. TX are only for publishers, not consumers,  
> thus the only way to implement TX behavior on the consumer side is  
> by not sending ACK. Is that correct?
>
> Since the spec is "completely silent" on the 'ordering', does that  
> mean that when I retrieve messages initially and they come in order  
> it is just a coincidence?
> I was under the impression that Queue semantics imply FIFO ordering,  
> regardless of which spec implements such Queue. Am I missing  
> something?
>
> Cheers
> Oleg
>
>
> On Jun 6, 2010, at 1:32 PM, Matthew Sackman wrote:
>
>> On Sun, Jun 06, 2010 at 09:58:20AM -0700, Oleg Zhurakousky wrote:
>>> I have a simple test where I receive 20 messages in the order in  
>>> which they came in, then rollback each and every one of them.
>>>
>>> Upon the next attempt to receive messages the order is completely  
>>> arbitrary. Is this by design?
>>
>> Yes, pretty much. Not quite sure what you mean by rollback though:
>> Transactions are only on what you send to the server, not what it  
>> sends
>> to you. I suspect you're not meaning to use transactions and are
>> actually just closing the connection or channel on which you've  
>> done the
>> consume, which will cause all unacked messages to be requeued. If you
>> use basic.recover{requeue=true} then the order will be more  
>> predictable,
>> however, that's a facet of the design: the spec is completely  
>> silent on
>> the order, and you should not rely on RabbitMQ doing any particular
>> ordering.
>>
>> Matthew
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