[rules-users] Workaround: EventFactHandle retained in memory after FactCount reaches 0 for temporal-based rule

[Kent Anderson]

We have found a workaround that eliminates the leftover event (gone from Working Memory, but not from the JVM memory): 

The rule “forget it ever happened” (seen below) causes the problem.  Re-writing it to remove the check for RAISE in the LHS eliminated the memory leak.  Of course, our application requires the check for RAISE, so it can be accomplished by manually querying working memory from the RHS.  It’s ugly, but it resolved the issue.

query existsRaise($id)
	$raise : MyEvent( eventState == EventState.RAISE, eventId == $id )
end

rule "process clear"
	no-loop
when
	$clear : MyEvent(eventState == EventState.CLEAR, $clearId : eventId)
then
	QueryResults results = kcontext.getKieRuntime().getQueryResults( "existsRaise", $clearId );
	if (results.size() == 0) { 
		System.out.println( "Forwarding CLEAR(" + $clearId + ")" ); 
	} else {
        	System.out.println("Forgetting RAISE/CLEAR(" + $clearId + ")");
	        for (QueryResultsRow row : results){
        		MyEvent raise = (MyEvent) row.get ("$raise");
        		delete(raise);
		}
	}
	delete($clear);
end

This appears to be a similar situation to https://issues.jboss.org/browse/DROOLS-498.



On Jul 10, 2014, at 3:54 PM, Kent Anderson <kent.anderson at psware.com> wrote:

> Correction:  The original post did not include another rule that exists in the stream.  The memory leak does not appear unless both rules are active in the stream.
> 
> declare MyEvent 
>   @role(event) 
>   @timestamp(timestamp) 
> end 
> 
> /* If a RAISE is buffered for N seconds, send it out */
> rule "forward raise"
> 	no-loop
> 	duration (3s)
> when
> 	$raise : MyEvent(eventState == EventState.RAISE, $raiseId : eventId)
> then
> 	System.out.println("Forwarding RAISE(" + $raiseId + ")");
> 	delete($raise);
> end
> 
> /* When CLEAR, and buffered, clear them both out */
> rule "forget it ever happened"
> 	no-loop
> when
> 	$clear : MyEvent(eventState == EventState.CLEAR, $clearId : eventId)
> 	$raise : MyEvent(eventState == EventState.RAISE, eventId == $clearId)
> then
> 	System.out.println("Forgetting RAISE/CLEAR(" + $clearId + ")");
> 	delete($clear);
> 	delete($raise);
> end
> 
> 
> On Jul 10, 2014, at 2:50 PM, Kent Anderson <kent.anderson at psware.com> wrote:
> 
>> The following rule produces a memory leak in Drools 6.1.0-SNAPSHOT:
>> 
>> (Stream mode)
>> 
>> declare MyEvent 
>>   @role(event) 
>>   @timestamp(timestamp) 
>> end 
>> 
>> /* If a RAISE is buffered for N seconds, send it out */
>> rule "forward raise"
>> 	no-loop
>> 	duration (3s)
>> when
>> 	$raise : MyEvent(eventState == EventState.RAISE, $raiseId : eventId)
>> then
>> 	System.out.println("Forwarding RAISE(" + $raiseId + ")");
>> 	delete($raise);
>> end
>> 
>> 
>> I see the rule fire as expected, printing out the message 3 seconds after the event is added into the session.  While the event is waiting, I see a FactCount of 1 in the session.  After the rule fires, the fact count goes to 0.  However, using JVisualVm, querying the heap dump shows 1 instance of MyEvent, referenced by an EventFactHandle and several other Drools objects.
>> 
>> Is this a bug, or is there a better way to write this rule so Drools’ internals let go of the object after it is no longer a fact?
>> 
>> <PastedGraphic-1.png>
>> 
>> <PastedGraphic-2.png>
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> 
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