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Subject Re: Dynamic message selectors and message scheduling
Date Sun, 13 Aug 2006 19:33:09 GMT
One option in AMQP would be to write a custom exchange to handle the
concept of delivery at a scheduled time. Exchanges are effectively an
extension point in the protocol so that you can customise delivery

The Glasgow broker currently doesn't have a well defined API to allow the
average end user to plug in new exchanges but this is definitely something
I think we will want to get to. Getting use cases such as yours definitely
helps us understand what type of thing users might want to be able to do in
an exchange.


                      "Noel J. Bergman"                                                  
                      <        To:       <>
                      >                        cc:                                    
                                               Subject:  Dynamic message selectors and message
                      13/08/2006 20:14                                                   
                      Please respond to                                                  

In the thread titled "RE: [Proposal] Blaze", James Strachan wrote:

>  Noel J. Bergman <> wrote:
> > Totally unrelated ... JMS has the ability to create a message filter,
> > one of the limitations is that the filter is applied when the receiver
> > created, rather than when a get operation is executed.  This makes
> > the push receiver case, but is limiting for the pull receiver case.
> > AMQP have anything to say about this aspect of messaging, or does it
> > strictly in the messaging provider space, and away from the client API?

> Could you explain a little more about your use case - it sounds
> interesting :). Do you only want to fetch a single message with a
> different filter per message, or just change the fliter from time to
> time. If its the latter then creating JMS consumers is pretty cheap &
> you can use any JMS to do that. Though the former, there's no 'give me
> a message using filter X' type operation.

Sorry for the delayed response.  Been busy on many fronts.

My particular use case involves selecting the next message in the
destination whose scheduled time is less than or equal to now.  If there
were a "now" operation available in the query language, I wouldn't have to
change the selector, but the expression would still have to be constantly
reevaluated.  And in that case, I'd want both pull and push behavior to be

One alternative is writing a broker to handle scheduling, which means
posting all messages intended to be rescheduled to the broker, which would
post them back when the schedule time occurs, thus handling scheduling in a
similar manner to how MQ handles subscriptions.

             --- Noel

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