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JMS Consumer (onMessage()) delay in getting message from Oralce AQ

I have an application where I have implemented Oracle AQ. I ran in to a behavior where average time for processing varied as depicted in graph below:



In above graph when volume of orders was less, average processing time came out to be more whereas when load increased with time, average time for processing got constant and then when volume started declining, time again started increasing.

 I analyzed the behavior and found that there is delay in message consumption after message has been produced to AQ. On further analysis I found that AQjmsListenerWorker goes for sleep if message is not available for consumption and sleep time doubles each time (up to peak limit) if message is not available for consumption. Thus optimizing resource utilization if there is no messages in AQ for consumption.

On enabling (-Doracle.jms.traceLevel=6) diagnostics logs for aq api. 

 I analyzed that Listener thread sleep time doubles till 15000 ms (15 sec), starting with default value 1000 ms, if null message is received from AQ. See below excerpt from logs:

 Thread-7 [Fri Oct 10 15:55:32 IST 2014] AQjmsListenerWorker.dispatchOneMsg:  Received the message: null message
Thread-7 [Fri Oct 10 15:55:32 IST 2014] AQjmsListenerWorker.doSleep:  try to wait for 1000 milliseconds
Thread-8 [Fri Oct 10 15:55:33 IST 2014] AQjmsListenerWorker.dispatchOneMsg:  Received the message: null message
Thread-8 [Fri Oct 10 15:55:33 IST 2014] AQjmsSimpleScheduler.feedData:  Got a null message, the sleep time is doubled to 2000
Thread-7 [Fri Oct 10 15:55:33 IST 2014] AQjmsListenerWorker.doSleep:  try to wait for 2000 milliseconds
...........

 Thread-7 [Fri Oct 10 15:55:47 IST 2014] AQjmsListenerWorker.dispatchOneMsg:  Received the message: null message
Thread-7 [Fri Oct 10 15:55:47 IST 2014] AQjmsSimpleScheduler.feedData:  Got a null message, the sleep time is doubled to 15000
Thread-7 [Fri Oct 10 15:55:47 IST 2014] AQjmsListenerWorker.doSleep:  try to wait for 15000 milliseconds

 So when volume was less sleep time was more.

 reference:- https://community.oracle.com/thread/2535275

 To reduce the sleep time I set below system properties. Thus making minimum start time to 100 ms which will double up to 4000 ms.
-Doracle.jms.minSleepTime=100

-Doracle.jms.maxSleepTime=4000

Sleep time is again set to 0 when a not null message is de-queued.

 Thread-7 [Fri Oct 10 15:59:18 IST 2014] AQjmsListenerWorker.dispatchOneMsg:  Received the message: D3DD9DC7EB894ABC915CE80C180C25D5

Thread-7 [Fri Oct 10 15:59:18 IST 2014] AQjmsSimpleScheduler.feedData:  Got a non null message, the sleep time is reset to 0



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