Dont forget there are two heaps. This video: http://www.youtube.com/watch?v=FLcXf9pO27w really explains it well.
Also, unless you want to totally manage garbage collection, letting the JVM decide the best fit is generally better. I run using these, your mileage may vary. (ps: If you want 1 gig, just say 1G) -XX:MaxTenuringThreshold=3 -XX:SurvivorRatio=24 -XX:+UseTLAB -XX:+UseConcMarkSweepGC -XX:+CMSClassUnloadingEnabled -XX:+UseParNewGC -XX:ReservedCodeCacheSize=50m -Xms512m -Xmx1G -Xss128k I realize the G1 collector you are using may obviate some of my params, but not all. hth.. -- View this message in context: http://activemq.2283324.n4.nabble.com/Activemq-heap-space-issue-activemq-5-8-c-stomp-tp4680436p4680708.html Sent from the ActiveMQ - User mailing list archive at Nabble.com.