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From Gordon Sim <g...@redhat.com>
Subject Re: Any way Qpid could preserve messages in TOPICS. Possibility ?
Date Thu, 15 Aug 2013 08:44:24 GMT
On 08/14/2013 07:55 PM, Rajesh Khan wrote:
> It seems like we are running into a requirement and I wanted to know if
> there was a way for TOPICS to preserve the last message Initially I was
> using LVQ which was really great however due to acknowledging messages and
> the delay we get because of that I moved to using QPID topics instead of
> queues. Now I want to know if there is a way of preserving the last message
> in a topic or if there is a way of disabling receive acknowledgment in
> Queues.

The distinction between queue and topic is a slightly fuzzy one. In JMS 
of course they represent two distinct messaging patterns. In pre 1.0 
AMQP, there is no concept of a 'topic' - generally the topic pattern as 
understood in JMS is implemented by binding a queue per subscription to 
an exchange.

However, another way of getting a similar pattern is  using a queue to 
which subscribers connect as 'browsers' (non-destructive, non-competing 
consumers of the messages). Used in this mode the LVQ is essentially a 
topic that retains the last message for a given key value.

For browsers on a queue, the acknowledgement isn't actually needed in 
that case.

For competing, i.e. destructive consumers, the acknowledgement can be 
implied meaning no explicit acknowledgement needs to be issued. To do 
this you would put 'reliability: unreliable' in your link options in the 
address with which the receiver was created.

I am however curious also as to the delay you were observing. If 
acknowledging every n messages, and doing so asynchronously, I would not 
expect a very large impact on throughput and certainly no 'delay' (as I 
understand the term).


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