[rabbitmq-discuss] is anybody using 'immediate' publish?

Randall Richard randall at trellisapp.com
Fri Sep 14 14:20:32 BST 2012

Matthias, thanks for the explanation.  Considering your points below, I now
have a better understanding on your thought that the actual use-cases and
practicality to publish messages with the immediate flag are minimal.  In
light of the details, I won't be using it -- faster mirrored queues sounds
better to me.  :o)


On Fri, Sep 14, 2012 at 8:48 AM, Matthias Radestock
<matthias at rabbitmq.com>wrote:

> Richard,
> On 14/09/12 13:34, Randall Richard wrote:
>> Admittedly, I'm not fully aware of exactly how it works.  It would be
>> helpful to have a better understanding of the semantics.  Can you
>> explain what the publisher is notified of (if anything?) when there are
>> 10 queues bound to an exchange named HighPriority, a message with
>> immediate flag true is published to HighPriority, and 7 out of the 10
>> queues have the message consumed immediately.
> No notification is sent to the publisher in that case. A basic.return is
> only sent if *no* queues were able to send the message to a consumer
> immediately.
> Here are a few more warts about 'immediate':
> - while a message might get sent out to a consumer straight away, there is
> of course no guarantee that such a message will reach the consumer, get
> processed and ack'ed. If any of these steps go wrong the message will end
> up in the queue (unless the consuming happened with no-ack, in which case
> it is simply lost), even though supposedly it was delivered immediately.
> - a queue can have a consumer and yet 'immediate' delivery may fail (and a
> basic.return issued) because:
> a) the consumer isn't quick enough and a backlog of messages has built up,
> b) the consumer has configured a 'basic.qos' prefetch count and that the
> limit has been reached
> - the interaction with transactions is not at all obvious. This does apply
> to 'mandatory' too though. See http://www.rabbitmq.com/**semantics.html#tx<http://www.rabbitmq.com/semantics.html#tx>
> Regards,
> Matthias.
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