Quinn, Dan wrote:

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.

no, after a query the memory should return to before the query was executed. If it's not, then there is a memory leak, maybe the retracting of the query driver is not happening. If you look at the query method, it just inserts a DroolsQuery object and retracts it and gathers up the results inbetween. If you have jprofiler you can have a good idea if the DroolsQuery object is getting GC'd, or if they are building up.

Mark

Thanks,

Dan

Daniel Quinn

Fedex - Custom Critical

Software Specialist I

234.310.4090(x2586)

From: rules-users-bounces@lists.jboss.org [mailto:rules-users-bounces@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@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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