[rules-users] rules-users Digest, Vol 63, Issue 60

[Shur, Bob]

I don't understand either of these answers. All of the facts are in a list of facts passed into ksession.execute, like this:

	        final StatelessKnowledgeSession ksession = kbase.newStatelessKnowledgeSession();
	        List<Object> facts = createPosts();  
	        if (facts.size() == 0) break;
	        long t0 = System.currentTimeMillis()/100;
	        ksession.execute(facts);   
	        long t1 = System.currentTimeMillis()/100;
	        System.out.println("Elapsed time: " + (t1 - t0));

There are no more facts getting created during rules processing. The whole drl file is:

rule "collect"
when
	$a : ArrayList(size > 0) from collect(Post());
then
	System.out.println("Number of posts: " + $a.size());
	System.out.println("DONE");
end

Why is the collect happening more than once? Actually I don't think it is, else I would be seeing more than one printout.

I agree that I could probably find a way to do without the list, but I would still like to understand why this is n-squared. I was actually planning to explore the performance of various ways to compute the minimum of a large number of objects. I was surprised to find that I was already up to n-squared just creating the list.

> ------------------------------
> 
> Message: 3
> Date: Mon, 13 Feb 2012 20:59:20 +0100
> From: Wolfgang Laun <wolfgang.laun at gmail.com>
> Subject: Re: [rules-users] Performance of collect seems to be
> 	n-squared
> To: Rules Users List <rules-users at lists.jboss.org>
> Message-ID:
> 	<CANaj1LeAnD-
> kYngQqTzo1XoOh4V8tnqo5A+9CkVR6xPmK4gxMA at mail.gmail.com>
> Content-Type: text/plain; charset="iso-8859-1"
> 
> Repeatedly creating this ArrayList is bound to be O(n2).
> 
> Why do you want the Post facts as a List? There may be better ways for
> achieving your goal.
> 
> -W
> 
> 
> On 13 February 2012 20:49, Shur, Bob <robert.shur at hp.com> wrote:
> 
> > I have a simple class Post { int id; ... }. I insert some number of
> them
> > as facts and then call ksession.execute(facts);
> >
> > The whole drl file (except for package and import statements) is:
> >
> > rule "collect"
> > when
> >        $a : ArrayList(size > 0) from collect(Post());
> > then
> >        System.out.println("Number of posts: " + $a.size());
> >        System.out.println("DONE");
> > end
> >
> > The time it takes to run is n-squared in the number of posts. For
> 4000,
> > 8000, 16000, 32000, 64000 posts the time is (in 1/10 seconds):
> >
> > 4, 14, 56, 220, 852
> >
> > Is this expected? Is there a better way for me to do the collect?
> >
> >
> > _______________________________________________
> > rules-users mailing list
> > rules-users at lists.jboss.org
> > https://lists.jboss.org/mailman/listinfo/rules-users
> >
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> ------------------------------
> 
> Message: 4
> Date: Mon, 13 Feb 2012 15:12:12 -0500
> From: Edson Tirelli <ed.tirelli at gmail.com>
> Subject: Re: [rules-users] Performance of collect seems to be
> 	n-squared
> To: Rules Users List <rules-users at lists.jboss.org>
> Message-ID:
> 	<CAD7AJnf9mZcm77o3uf+EbigEVZzpgo5UJkKeyR0M0r1f3io1gw at mail.gmail.c
> om>
> Content-Type: text/plain; charset="iso-8859-1"
> 
>    Just FYI, the array list is created once and reused with incremental
> addition/removal of elements.
> 
>    The problem is that the engine does not know when you are done
> inserting
> all the Post facts, so each post inserted is propagated down the
> network
> with the cancellation and reactivation of the rule.
> 
>    This is one of those situations where a use of a control fact might
> be
> recommended, if you are inserting Post facts in batches. E.g.:
> 
> rule X
> when
>      exists( AllPostsInserted() )
>      $a : ArrayList(size > 0) from collect(Post());
> then
> ...
> end
> 
>    Edson
> 
> 
> 2012/2/13 Wolfgang Laun <wolfgang.laun at gmail.com>
> 
> > Repeatedly creating this ArrayList is bound to be O(n2).
> >
> > Why do you want the Post facts as a List? There may be better ways
> for
> > achieving your goal.
> >
> > -W
> >
> >
> >
> > On 13 February 2012 20:49, Shur, Bob <robert.shur at hp.com> wrote:
> >
> >> I have a simple class Post { int id; ... }. I insert some number of
> them
> >> as facts and then call ksession.execute(facts);
> >>
> >> The whole drl file (except for package and import statements) is:
> >>
> >> rule "collect"
> >> when
> >>        $a : ArrayList(size > 0) from collect(Post());
> >> then
> >>        System.out.println("Number of posts: " + $a.size());
> >>        System.out.println("DONE");
> >> end
> >>
> >> The time it takes to run is n-squared in the number of posts. For
> 4000,
> >> 8000, 16000, 32000, 64000 posts the time is (in 1/10 seconds):
> >>
> >> 4, 14, 56, 220, 852
> >>
> >> Is this expected? Is there a better way for me to do the collect?
> >>
> >>
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