It would almost seem as though the collection is a sort of sub rule that fires for every insert, and generates temporary fact collections based on the results, and so, even though you are inserting all the facts before calling the execute in the stateless session, each and every single fact is being evaluated for the collect sub-rule to build the new collections, and then those new collections are fed into the actual rule as temporary facts unique to that rule. And that perhaps this is the source of the n-squared processes. Have you tried a more literal approach like this? (based on your comment that you are looking for the minimum) (assuming there is a property called Value that you are looking to get the minimum of) rule "minimum" when Post($v: value) not Post(value <= $v) then System.out.println("Minimum value: " + $v); end rule "maximum" when Post($v: value) not Post(value >= $v) then System.out.println("Maximum value: " + $v); end Of course, this has not direct ration to what you are trying to do, but rather, I am focusing on your comment that you trying to focus on computing the minimum of a large collection of objects. I wonder if accumulate might do a better job in solving your original problem, since accumulate could allow you to calculate min, max, average, count, sum, return collections as List and Set of data.. Take a look at section 5.8.3.6.4.1 of the Drools Expert manual for details on use, and 5.8.3.6.4.2 for details on creating your own functions which could do all of these in one, which would greatly reduce the number of iterations through your source collection. -----Original Message----- From: rules-users-bounces(a)lists.jboss.org [mailto:rules-users-bounces@lists.jboss.org] On Behalf Of Shur, Bob Sent: Monday, February 13, 2012 3:06 PM To: rules-users(a)lists.jboss.org Subject: Re: [rules-users] rules-users Digest, Vol 63, Issue 60 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(a)gmail.com&gt; > Subject: Re: [rules-users] Performance of collect seems to be > n-squared > To: Rules Users List <rules-users(a)lists.jboss.org&gt; > Message-ID: > <CANaj1LeAnD- > kYngQqTzo1XoOh4V8tnqo5A+9CkVR6xPmK4gxMA(a)mail.gmail.com&gt; > 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(a)hp.com&gt; 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(a)lists.jboss.org > > https://lists.jboss.org/mailman/listinfo/rules-users > > >