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From yg_cvg <>
Subject another question about networks of brokers
Date Tue, 18 Dec 2007 23:02:06 GMT

This is to follow up on
(but reading that isn't necessary).

Let's say I have a big graph of brokers connected to each other and producer
A on broker A' sending a message to topic T.  Further, let's say I have
consumer B subscribed to T on broker B', which is a few brokers away from A'
in the graph.  Let's also say that NO other brokers in the graph (even those
on the path(s) between A' and B') have any consumers subscribed to topic T.

I know the message will get to B if I set networkTTL to be high enough.  (I
tried it, and of course it works.)

My question is, in this process, where does the physical message actually
get sent over the network?  (Again, I realize that, regardless, it will get
everywhere it NEEDS to go, but the question here is will it also go places
it does NOT needs to go.)

Does it go to EVERY broker in the graph (regardless of who's subscribed to
what, if anything), or does it only go through the shortest path of brokers
between A' and B'?

If the latter, how is that accomplished?  Does every broker in the graph
KNOW which remote brokers around it are subscribed to which topics, so it
determines where to forward the messages based on that?

This will be useful for designing our (potential) distributed network of
ActiveMQ brokers.  It will let us estimate the amount of traffic that will
be going through the system.

P.S.  In the above link, raj says that if EVERY broker in the graph has a
consumer subscribed to T, then the message is physically sent everywhere in
a BFS (breadth-first search) fashion.  But the above question is different:
what happens when only SOME brokers have consumers subscribed to T.
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