The use case is to limit the pending message length by memory usage and to fail the producer with an exception when the memory limit (or 70% of the memory limit) is reached. The limit can be reached very easily with a fast producer and slow (or no) consumer.
In activemq XML configuration use:
<memoryUsage limit="20 mb">
</systemUsage>If the attribute is incorrectly added to the top level element, it is ignored and the result is that a producer will experience the default "wait for space to become available" behaviour and will hang.
Note to self, be sure to double check where XBean attributes are specified!