A little while back someone posted a message about an OutOfMemoryError problem when marshalling a knowledgebase containing rules with NOT conditions: http://drools-java-rules-engine.46999.n3.nabble.com/OutOfMemoryError-on-m... Someone created a JIRA issue for him, which says that it's fixed, but there are two comments on it now saying that it is not (in 5.1.1), one of them being mine: https://jira.jboss.org/browse/JBRULES-2453 I don't know the recommended procedure for requesting a bug to be reopened or cloned, which is why I am posting here. My apologies. I am quite convinced that there is still a bug in that code. For illustration, below is a little rule base which lets me reproduce the issue. The three fact types are pretty simple, and I insert 2 facts for DCMSeries and about 630 for DCMInstance. The marshalling breaks if done after inserting the facts and before a call to fireAllRules. Marshalling afterwards does not consistently exhibit this issue. Eliminating the "not" condition also "fixes" the problem. Uli package mypackage import somepackage.DCMInstance import somepackage.DCMSeries import somepackage.StackingOrder rule "Stack Default" when        DCMSeries( $suid : uid )        DCMInstance( seriesUID == $suid, $iuid: uid )        not StackingOrder(instanceUID == $iuid) then end -- View this message in context: http://drools-java-rules-engine.46999.n3.nabble.com/OutOfMemoryError-duri... Sent from the Drools - User mailing list archive at Nabble.com. _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users