Hi Len,

Here are some reasons that a messaging system might be better for this 
kind of application:

1. Updates are made precisely when something has changed at the source. 
This eliminates the need for clients to poll just in case something has 
changed, which accounts for a lot of unnecessary polling.

2. Guaranteed delivery is supported.

3. Higher performance network protocols can be used.

I think the existence of open source, high performance, reliable 
messaging systems has the potential to significantly change the way 
people write a lot of systems, including a lot of XML-based systems. 
This is one of the reasons I'm at Red Hat now.

Jonathan

Len Bullard wrote:
> Ok, I will reveal my massive ignorance but that's fine.  I was considering
> the tradeoffs between querying the database to find anything new versus
> polling the directory and having the database publish when it changes since
> it will know.   The question seems to turn on where the most cycles are
> being consumed: polling and file i/o vs querying on a scheduled basis.   In
> ASP (another MSThrall gig), there are timers for refreshing a control so
> hooking that up and querying is quite easy even for me.  OTOH, RSS readers
> also handle that nicely.
>
> I am somewhat stuck with the solutions I proposed, but for the sake of
> learning and keeping signal high here on the big list, why is a messaging
> system better?  
>
> len
>
> (Personal Note:  It is good to be back on the ground level of software
> instead of schlepping answers back and forth among writers and managers in
> the executive suites.)
>
> From: Jonathan Robie [mailto:jonathan.robie@r...] 
>
> Hi Len,
>
> I think of both feeds and SQL queries as pull technologies - the user 
> checks the feed to see if there's anything new, or does a query to see 
> if there's anything new.
>
> For this kind of push application, I'd be more inclined to use a 
> messaging system that has both guaranteed delivery and really good 
> performance. One of my current hobby horses is the AMQP protocol, which 
> will be supported by Red Hat Messaging, an open source implementation 
> for enterprise level applications. Early versions are available to 
> download and play with.
>
> Check it out here:
>
> http://labs.jboss.com/rhmessaging/
> http://rhm.et.redhat.com/page/Getting_Started_With_RHM
>
> Jonathan
>  
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