The following simple code reproduces the growth of java.lang.ref.WeakReference objects in the heap: public static void main(String[] args) throws Exception { while (true) { java.util.logging.Logger.getAnonymousLogger(); Thread.sleep(1); } } Here is the output of jmap command within a few seconds interval: user@t1007:~ jmap -d64 -histo:live 29201|grep WeakReference 8: 22493 1079664 java.lang.ref.WeakReference 31: 1 32144 [Ljava.lang.ref.WeakReference; 106: 17 952 com.sun.jmx.mbeanserver.WeakIdentityHashMap$IdentityWeakReference user@t1007:~ jmap -d64 -histo:live 29201|grep WeakReference 8: 23191 1113168 java.lang.ref.WeakReference 31: 1 32144 [Ljava.lang.ref.WeakReference; 103: 17 952 com.sun.jmx.mbeanserver.WeakIdentityHashMap$IdentityWeakReference user@t1007:~ jmap -d64 -histo:live 29201|grep WeakReference 8: 23804 1142592 java.lang.ref.WeakReference 31: 1 32144 [Ljava.lang.ref.WeakReference; 103: 17 952 com.sun.jmx.mbeanserver.WeakIdentityHashMap$IdentityWeakReference Note that jmap command forces FullGC. JVM settings: export JVM_OPT="\ -d64 \ -Xms200m -Xmx200m \ -XX:MaxNewSize=64m \ -XX:NewSize=64m \ -XX:+UseParNewGC \ -XX:+UseConcMarkSweepGC \ -XX:MaxTenuringThreshold=10 \ -XX:SurvivorRatio=2 \ -XX:CMSInitiatingOccupancyFraction=60 \ -XX:+UseCMSInitiatingOccupancyOnly \ -XX:+CMSParallelRemarkEnabled \ -XX:+DisableExplicitGC \ -XX:+CMSClassUnloadingEnabled \ -XX:+PrintGCTimeStamps \ -XX:+PrintGCDetails \ -XX:+PrintTenuringDistribution \ -XX:+PrintGCApplicationConcurrentTime \ -XX:+PrintGCApplicationStoppedTime \ -XX:+PrintGCApplicationStoppedTime \ -XX:+PrintClassHistogram \ -XX:+ParallelRefProcEnabled \ -XX:SoftRefLRUPolicyMSPerMB=1 \ -verbose:gc \ -Xloggc:$GCLOGFILE" java version "1.6.0_18" Java(TM) SE Runtime Environment (build 1.6.0_18-b07) Java HotSpot(TM) Server VM (build 16.0-b13, mixed mode) Solaris 10/Sun Fire(TM) T1000