I've talked with edson and later mark a bit on IRC and they identified 3 issues which I created in JIRA: https://jira.jboss.org/jira/browse/JBRULES-2238 Accumulate should be implemented with left-input incremental so they don't start from scratch on every left-input retraction/assertion https://jira.jboss.org/jira/browse/JBRULES-2239 Batching accumulate to avoid wasteful re-propagations https://jira.jboss.org/jira/browse/JBRULES-2240 True modify You can easily benchmark any before and after your changes with this "run configuration": - Project: drools-solver-examples - Run configuration name: ExaminationBenchmarkApp short - Main class: org.drools.solver.examples.itc2007.examination.app.ExaminationBenchmarkApp - VM parameters: -Xms256m -Xmx512m -server - Program parameters: short - Working directory: .../drools/drools-solver/drools-solver-examples If you run this, it will do a 100 steps of the examination problem (on my pc this takes 71s). The last line of output will be like this: 2009-08-08 10:10:55,499 [main] INFO Solved at step index (99) with time spend (71524) for best score (0hard/-7545soft). The "time spend (71524)" tells you how many milliseconds it took. The "best score (0hard/-7545soft)" should never change in any changes you make. You'll want to make changes in the examinationScoreRules.drl file: drools/drools-solver/drools-solver-examples/src/main/resources/org/drools/solver/examples/itc2007/examination/solver/examinationScoreRules.drl There are 3 rules of interest in there that use accumulate: rule "roomCapacityTooSmall" // TODO improve performance, as it takes 50% of the performance rule "hardConstraintsBroken" rule "softConstraintsBroken" PS: Note that drools-solver on trunk is fixed on drools-core 5.0.1 in the drools-solver pom.xml (you can easily change this). -- With kind regards, Geoffrey De Smet