activemq systemUsage xml configuration and sendFailIfNoSpace ...

I was caught out with this twice in 24hrs. The systemUsage sendFailIfNoSpace attribute must be configured on the XBean element content, not on the element wrapper.
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:

<systemUsage>

 <systemUsage sendFailIfNoSpace="true">

   <memoryUsage>

     <memoryUsage limit="20 mb">

   </memoryUsage>

 </systemUsage>

</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!