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From Rob Davies <>
Subject Re: network of brokers internals
Date Tue, 05 Jan 2010 08:15:16 GMT

Some background - which may help.
Information about subscriptions are passed dynamically using advisory  
messages. Information about the current, active subscriptions are  
forwarded - to the remote broker - as are arrivals of new  
subscriptions and departures of old. By default information about  
Queues and durable subscribers (even if not active) are also  
forwarded. More info here:
Bit confused by filters - there are network filters - which filter out  
destinations on a network - but I think you mean selectors ? Selectors  
are part of the JMS spec and can be optionally applied to a  
Rest in-lined:
On 4 Jan 2010, at 20:42, user9876 wrote:

> Hi could someone please explain at a relatively low level how the  
> Network of
> Brokers works.  I currently have quite a simple understanding that  
> once a
> network is set up, a client can publish to any broker in the network  
> and
> that message will be forwarded to any subscriptions present on any  
> other
> broker.  I also believe these subscriptions can have filters.
> I know this is quite a broad question so the particular questions I  
> have
> are:
> When a client subscribes to a topic on one broker, how are the other  
> brokers
> in the network made aware of this new subscription and how do they  
> store the
> subscriptions and the individual filters (predicates)?
Subscriptions are dynamic - so information is cached in memory.  
However on re-start of a broker - it will query its message store for  
queues and durable subscribers - creating a proxy active subscriber  
for each.
Filters are defined in the local configuration of the broker.  
Selectors on subscriptions are generally ignored.
> Does each broker in the network hold replicated information of the
> subscriptions present on the network?
Yes it does.
> If two subscriptions exist on one broker with different filters,  
> will a
> message be sent once only across the network? And generally how are  
> the
> messages routed?
The message will be sent once - and the selector applied locally
> -- 
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Rob Davies
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