Sample JVM Settings

export JAVA_OPTS="-Xms1024m -Xmx2048m -Xss1024k -XX:MaxPermSize=256m -XX:NewSize=256m -XX:+UseConcMarkSweepGC -Dalfresco.home=/opt/alfresco -Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.ssl=false -Djava.awt.headless=true"

export JAVA_OPTS="${JAVA_OPTS} -server"
export JAVA_OPTS="${JAVA_OPTS} -Xms6600m -Xmx6600m -XX:PermSize=256m -XX:MaxPermSize=256m -XX:NewSize=2990m -XX:ReservedCodeCacheSize=128m"
export JAVA_OPTS="${JAVA_OPTS} -XX:+UseParNewGC -XX:+UseConcMarkSweepGC -XX:CMSInitiatingOccupancyFraction=80"
export JAVA_OPTS="${JAVA_OPTS} -Dalfresco.home=${ALF_HOME} -Dcom.sun.management.jmxremote -Dfile.encoding=UTF8"

http://javarevisited.blogspot.co.uk/2011/05/java-heap-space-memory-size-jvm.html