Producer Flow ControlIn ActiveMQ 4.x flow control was implemented using TCP flow control. The underlying network connection of throttled consumers was suspended to enforce flow control limits. This strategy is very efficient but can lead to deadlocks if there are multiple producers and consumers sharing the same connection. As of ActiveMQ 5.0, we can now individually flow control each producer on a shared connection without having to suspend the entire connection. Messages that are sent synchronously will automatically use per producer flow control. For producers that use Async Sends, you will need to configure the ProducerWindowSize connection option so that even async messages are flow controlled per producer. ActiveMQConnectionFactory connctionFactory = ... connctionFactory.setProducerWindowSize(1024000); The ProducerWindowSize is the maximum number of bytes of data that a producer will transmit to a broker before waiting for acknowledgment messages from the broker that it has accepted the previously sent messages. In other words, this how you configure the producer flow control window that is used for async sends. You can disable flow control by setting the producerFlowControl flag to false on a destination policy in the Broker configuration - e.g. <destinationPolicy>
<policyMap>
<policyEntries>
<policyEntry topic="FOO.>" producerFlowControl="false" memoryLimit="1mb">
<dispatchPolicy>
<strictOrderDispatchPolicy/>
</dispatchPolicy>
<subscriptionRecoveryPolicy>
<lastImageSubscriptionRecoveryPolicy/>
</subscriptionRecoveryPolicy>
</policyEntry>
</policyEntries>
</policyMap>
</destinationPolicy>
How Producer Flow Control worksIf you are sending a persistent message (so that a response of the OpenWire Message is expected then the broker will send the producer a ProducerAck AdvantageSo a nice producer might wait for a producer ack before sending more data, to avoid flooding the broker (and forcing the broker to block the entire connection if a slow consumer occurs). To see how this works in source code, check out the ActiveMQMessageProducer Though a client can ignore the producer ACKs altogether and the broker should just stall the transport if it has to for slow consumer handling; though this does mean it'll stall the entire connection. |
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