[rules-users] Need clarification on how event expiration offset is calculated in 5.3.0.FINAL

[Edson Tirelli]

   Scott,

   The event expiration algorithm in Drools works with compile time
analysis of temporal constraints. It calculates the transitive closure on
the temporal intervals created by each temporal constraint and from that it
infers the required time for an event to stay in memory, expiring them
after that. Some interactions are pretty hard to calculate manually, but as
you already realized, you can enable the Drools MBeans and use jconsole (or
visualvm as you mentioned) to inspect them.

    In your case, first things first, I assume you are running the engine
in STREAM mode? the default is CLOUD mode, and in CLOUD mode there is no
expiration of events. Second, there was a bug in one of the released
versions of Drools (I think 5.2 or 5.3) that was fixed after where the
calculation was wrong if the events were in different packages. Finally,
you are using external timestamps for the events (on its attributes), so
make sure your clock is in line with the externally timestamped events.

    If everything I mentioned is working as expected and your events are
still not being expired, please try adding an explicit expiration policy
(e.g., @expires( 1m ) ), and submit a bug (JIRA) with your findings.

    Edson

2011/12/7 Scott Embler <stembler at gmail.com>

> Hi,
>
> I've recently started using some of the temporal operators that drools
> supports (coincides, starts, finishes, during) and have had trouble with
> events not being expired, causing severe memory consumption.
> I'd first like to make sure that I'm using these operators appropriately,
> so as a test case I have rules like:
>
> declare A
>   @role( event )
>   @timestamp( timestamp )
>   @duration( duration )
> end
>
> declare B
>   @role( event )
>   @timestamp( timestamp )
>   @duration( duration )
> end
>
> rule "coincides events"
> when
>   $a: A() from entry-point "a"
>   $b: B(this coincides $a) from entry-point "b"
> then insert("coincides"); end
>
> With classes like:
>
> public class A{
>         public final long timestamp;
>         public final long duration;
>         public A(long timestamp, long duration){
>             this.timestamp = timestamp;
>             this.duration = duration;
>         }
> }
>
> //B is identical to A.
>
> Using a knowledge base configured with stream mode, and a knowledge
> session with a pseudo clock I'd run this test:
>
> A a = new A(0, 1000);
> B b = new B(0, 1000);
>
> entryPointA.insert(a);
> entryPointB.insert(b);
> clock.advanceTime(1000, TimeUnit.MILLISECONDS);
> ksession.fireAllRules();
>
> In this test I'm expecting that the rule will fire to insert "coincides"
> and expire both A and B.  But instead, "coincides" is inserted, B is
> expired, but A remains in memory permanently.  If I use jvisualvm to
> inspect the expirationOffset for A, I see that it is the Long.MAX value of
> 9223372036854775807.  This behavior persists even after adding an explicit
> expiration to A.  I was under the impression that the offset would be zero
> (of close to it) since Drools would only need to retain A until the clock
> reaches A's endTimestamp.  The documentation does not cover the calculation
> of event expiration in great detail, so have I missed something?  Thanks in
> advance.
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>
>


-- 
  Edson Tirelli
  JBoss Drools Core Development
  JBoss by Red Hat @ www.jboss.com
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