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From jahlborn <jahlb...@gmail.com>
Subject Correctly configuring a network of brokers
Date Thu, 05 Nov 2015 21:02:52 GMT
So I've spent some time digging around the internet and experimenting with
our
setup, trying to determine the best configuration for a network of brokers.
There are a variety of things which seem to conspire against me: the
multitude
of configuration options present in activemq, options which seem to have no
"optimal" setting (each choice has different pros and cons), and
behavior/features which change over time such that old recommendations may
now
be irrelevant or no longer correct.  For reference, we are using a mesh
network of brokers, where consumers may arrive at any broker in the network.
We use topics, queues, and virtual queues.  We use explicit receive() calls
as
well as listeners.  We also utilize the "exclusive consumer" feature for
some
of our clustered consumers.  All messaging is currently durable.  Some
relevant configuration bits (changes from the defaults).

* using activemq 5.9.1
* advisory support is enabled
* PolicyEntry
** optimizedDispatch: true
* Using ConditionalNetworkBridgeFilterFactory
** replayWhenNoConsumers: true
** replayDelay: 1000
* NetworkConnector
** prefetchSize: 1
** duplex: false
** messageTTL: 9999

Alright, now that we got through all the context, here's the meat of the
question.  There are a bunch of configuration parameters (mostly focused in
the NetworkConnector), and it's not at all clear to me if my current
configuration is optimal.  For instance, although we had been using a
configuration similar to the above for about a year now (same as above
except
that messageTTL was 1), we only recently discovered that our exclusive
consumers can sometimes stop processing messages.  In certain cases, the
consumer would end up bouncing around and the messages would end up getting
stuck on one node.  Adding the messageTTL setting seems to fix the problem
(is
it the right fix...?).

* NetworkConnector
** "dynamicOnly" - i've seen a couple of places mention enabling this and
some
   indication that it helps with scaling in a network of brokers (e.g. [3]).
   The description in [1] also makes it sound like something i would want to
   enable.  However, the value defaults to false, which seems to indicate
that
   there is a down-side to enabling it.  Why wouldn't i want to enable this?
** "decreaseNetworkConsumerPriority", "suppressDuplicateQueueSubscriptions"
-
   these params both seem like "damned if you do, damned if you don't" type
   parameters.  The first comment in [2] seems to imply that in order to
   scale, you really want to enable these features so that producers prefer
   pushing messages to local consumers (makes sense).  Yet, at the same
time,
   it seems that enabling this feature will _decrease_ scalability in that
it
   won't evenly distribute messages in the case when there are multiple
active
   consumers (we use clusters of consumers in some scenarios).  Also in [2],
   there are some allusions to stuck messages if you don't enable this
   feature.  Should i enable these parameters?
** "networkTTL", "messageTTL", "consumerTTL" - until recently, we kept these
   at the defaults (1).  However, we recently realized that we can end up
with
   stuck messages with these settings.  I've seen a couple of places which
   recommend setting "networkTTL" to the number of brokers in the network
   (e.g. [2]), or at least something > 1.  However, the recommendation for
   "consumerTTL" on [1] is that this value should be 1 in a mesh network
(and
   setting the "networkTTL" will set the "consumerTTL" as well).
   Additionally, [2] seems to imply that enabling
   "suppressDuplicateQueueSubscriptions" acts like "networkTTL" is 1 for
proxy
   messages (unsure what this means?).  We ended up setting only the
   "messageTTL" and this seemed to solve our immediate problem.  Unsure if
it
   will cause other problems...?
** "prefetchSize" - defaults to 1000, but I see recommendations that it
should
   be 1 for network connectors (e.g. [3]).  I think that in our initial
   testing i saw bad things happen with this setting and got more even load
   balancing by lowering it to 1.

I think that about summarizes my questions and confusion.  Any help would be
appreciated!

[1] http://activemq.apache.org/networks-of-brokers.html
[2] https://issues.jboss.org/browse/MB-471
[3]
http://www.javabeat.net/deploying-activemq-for-large-numbers-of-concurrent-applications/




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