[rules-users] queries in Drools 5.0

[Quinn, Dan]

We are writing an app which has a large number of facts. This app also
needs to make lots of queries against working memory. Our memory
footprint seems to be expanding at an undesirable rate due to the number
of queries made against working memory. It is increasing at a rate where
after a couple of days the app will consume all the resources on the
machine. This app is stateful and needs to stay up for a long duration.
Rebooting it every couple of day to clean up working memory would not be
acceptable.
 
 It seems to me that the queries are being added to working memory as
facts, but the query is not retracted after its result is returned. Is
that true? Is there something I need to do so query facts are removed
after the results are returned to keep the size of working memory down?
 
Has this behavior changed since Drools 4.0.7. I don't recall seeing this
issue running against the older version of Drools.
 
Thanks,
Dan
 
Daniel Quinn
Fedex - Custom Critical
Software Specialist I
234.310.4090(x2586)
 

________________________________

From: rules-users-bounces at lists.jboss.org
[mailto:rules-users-bounces at lists.jboss.org] On Behalf Of David Sinclair
Sent: Friday, April 03, 2009 3:20 PM
To: Rules Users List
Subject: Re: [rules-users] Locating facts via slot values


Here you go WolfGang

rule shoot-3 
    when
            $h : Hunter( $target : target)
                  Animal(this == $target)
    then
       $h.shoot( $a );
       retract( $a );
end


2009/4/3 Wolfgang Laun <wolfgang.laun at gmail.com>


	Given a working memory containing a large number of rather
static facts which are from several subclasses (Ape, Bear,
Crocodile,...) of some base class (Animal) and a single fact of class
Hunter with a field target of type Animal, the shooting of an animal
might be written with a rule like this:
	
	rule shoot-1
	    when
	        ?h : Hunter( ?target : target )
	        ?a : Animal()
	        eval(?target == ?a)
	    then
	       ?h.shoot( ?a );
	       retract( ?a );
	end
	
	Avoiding eval (which is said to be inefficient), it could also
be written as
	
	rule shoot-2
	    when
	        ?a: Animal()
	        ?h : Hunter( target  == ?a )
	    then
	       ?h.shoot( ?a );
	       retract( ?a );
	end
	
	This, however, places the pattern with many instances up front,
which is (AFAIK) not so good in a Rete implementation.
	
	Which one is to be preferred in Drools?
	
	Ideally, one might want to write 
	
	rule shoot-3
	    when
	        ?h : Hunter( ?target : target )
	        ?a == ?target : Animal()                   ### not valid
DRL
	    then
	       ?h.shoot( ?a );
	       retract( ?a );
	end
	
	This avoids eval, has the single instance fact up front, but it
isn't available.
	
	-W
	
	
	
	
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