> The prefetch limit determines how many messages can be sent to a > consumer to be processed. The default value for the queue prefetch > limit is 1000. Oftentimes this limit is fine for fast consumers that > never slow down, but it can easily flood a slow consumer. This is why > we recommend adjusting the prefetch limit based on the consumer > behavior.
Hi Bruce, We've noticed the same behaviour as the OP and found that setting a prefetch limit of 1 on the network connector URL had no effect in limiting/balancing the message distribution. The reason was because the DemandForwardingBridgeSupport creates a "proxy" consumer for its local instance of the shared queue. This proxy consumer is what gets registered with the producer's instance of the shared queue and its only job is to receive and store the messages. Since the proxy consumer is detached from the actual consumer, with a prefetch of 1 it just spins as fast as possible receiving and storing the messages --- the only difference is that it sends back on ACK on each message as opposed to every 1000 messages. Is this your understanding as well regarding the effect of prefetch in a network of brokers? I'm guessing it's the reason why you suggested a custom dispatch policy? A similarly behaving scenario is when a producer generates say 10,000 messages into a shared queue and there are no consumers. Two consumers are then started at roughly the same time. We'd hoped that the consumers would a roughly equal number of messages, but instead we noticed that one consumer would tend to get all the messages. Again, the reason was that one consumer manages to start up slightly ahead of the other and the DemandForwardingBridgeSupport "proxy" consumer gobbles up all available messages as quickly as it can, regardless of the actual spead of its "actual" consumer. Unfortunately, this behaviour has been very problematic for us in regards to using distributed queues. We're hoping that there will be enough interest from other AMQ users to warrant the work to enhance the dispatching mechanism. -- View this message in context: http://activemq.2283324.n4.nabble.com/Configuring-Distributed-Queues-in-Store-Forward-Network-tp2967501p2968819.html Sent from the ActiveMQ - User mailing list archive at Nabble.com.
