[rules-users] Inconsistency in Drools' Performance (Version 5.5.0)

Hi, I have been trying to measure Drools'  5.5.0 performance for quite some time. I see that Drools' perform inconsistently in terms of CPU time. Please see the below code (modification of DroolsTest example): /*Code start*/ public class DroolsTest {     public static final void main(String[] args) {         try {             // load up the knowledge base             KnowledgeBase kbase = readKnowledgeBase();             // go !             for (int i = 0; i < 20; i++) {             Message message = new Message();             message.setMessage("Hello World");             message.setStatus(Message.HELLO);             long startTime = System.nanoTime();             StatefulKnowledgeSession ksession = kbase.newStatefulKnowledgeSession();             FactHandle handle = ksession.insert(message);             ksession.fireAllRules();             ksession.retract(handle);             System.out.println("Time taken is: " + (System.nanoTime()-startTime)/1000);             ksession.dispose();             }         } catch (Throwable t) {             t.printStackTrace();         }     }     private static KnowledgeBase readKnowledgeBase() throws Exception {         KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();         kbuilder.add(ResourceFactory.newClassPathResource("Sample.drl"), ResourceType.DRL);         KnowledgeBuilderErrors errors = kbuilder.getErrors();         if (errors.size() > 0) {             for (KnowledgeBuilderError error: errors) {                 System.err.println(error);             }             throw new IllegalArgumentException("Could not parse knowledge.");         }         KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase();         kbase.addKnowledgePackages(kbuilder.getKnowledgePackages());         return kbase;     }     public static class Message {         public static final int HELLO = 0;         public static final int GOODBYE = 1;         private String message;         private int status;         public String getMessage() {             return this.message;         }         public void setMessage(String message) {             this.message = message;         }         public int getStatus() {             return this.status;         }         public void setStatus(int status) {             this.status = status;         }     } } /** Code end**/ I have just added timing code to the DroolsTest.java program (provided by JBoss) and I am using Sample.drl file (provided by JBoss). The rules get executed correctly but the timings that I see are: Iteration 1: 103753 (we can ignore this as the classes get loaded during the first iteration) Iteration 2: 861 Iteration 3: 744 Iteration 4: 1350 Iteration 5: 718 Iteration 6: 651 Iteration 7: 661 Iteration 8: 668 Iteration 9: 648 Iteration 10: 3564 Iteration 11: 911 Iteration 12: 689 Iteration 13: 682 Iteration 14: 796 Iteration 15: 4236 Iteration 16: 774 Iteration 17: 772 Iteration 18: 722 Iteration 19: 713 Iteration 20:  697 I profiled it with Yourkit Profiler and the increase in time does not correspond to garbage collection. I also timed individual calls and found out that: - ksession.insert: takes consistent time - ksession.fireAllRules: inconsistent - kbase.newStatefulKnowledgeSession: inconsistent I see same inconsistency in performance when I integrate Drools with original project (which I can't share here). I also found that this has nothing to do with compiler optimizations. Why is there inconsistent performance? Is there anything that I am missing? Thank you.