Default settings lead to paging and high latency for non persistent pub/sub
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Key: AMQ-2400
URL: https://issues.apache.org/activemq/browse/AMQ-2400
Project: ActiveMQ
Issue Type: Bug
Components: Broker
Affects Versions: 5.3.0
Environment: N/A
Reporter: Colin MacNaughton
The current default config doesn't enable a memoryLimit or flow control for
topics which consequently leads to high latency and lower throughput.
I ended up tweaking the default config to limit destination sizes and enable
flow control as follows:
<destinationPolicy>
<policyMap>
<policyEntries>
<policyEntry topic=">" producerFlowControl="true" memoryLimit="1mb">
<pendingSubscriberPolicy>
<vmCursor/>
</pendingSubscriberPolicy>
</policyEntry>
<policyEntry queue=">" producerFlowControl="true" memoryLimit="1mb"/>
</policyEntries>
</policyMap>
</destinationPolicy>
The current default config was resulting in really high latencies in non
persistent pub sub tests (> 2 minutes!). With the new settings throughput
doubled and average latency dropped to 3 seconds.
However, it seems like there is some resistance to enabling flow control by
default: http://issues.apache.org/activemq/browse/AMQ-2318, as naïve users
might erroneously interpret this as a hang.
A possible compromise appropriate for the 5.3.0 release time frame would be to
log a warning the first time flow control is triggered for a destination, to
assist naive users in troubleshooting producer pauses.
More long term, it might be worth introucing a more sophisticated mechanism for
when we page to disk like only do so when there are no consumers connected. A
policy similar to this is already being pursued in the amq 6.0 prototype.
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