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: http://activemq.apache.org/networks-of-brokers.html
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
MessageConsumer
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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cheers,
Rob
Rob Davies
http://twitter.com/rajdavies
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