I have Cassandra server which has JVM setting -Xms4G -Xmx4G, but why top reports 15G RES memory and 11G SHR memory usage? I understand that -Xmx4G is only for the heap size. but it is strange that OS reports 2.5 times memory usage. Are there a lot of memory used by JNI? Please help to explain this.
cassy 2549 39.7 66.1 163805536 16324648 ? Sl Jan02 338:48 /usr/local/cassy/java/current/bin/java -ea -javaagent:./../lib/jamm-0.2.2.jar -XX:+UseThreadPriorities -XX:ThreadPriorityPolicy=42* -Xms4G -Xmx4G -Xmn1G*-XX:+HeapDumpOnOutOfMemoryError -Xss128k -XX:+UseParNewGC -XX:+UseConcMarkSweepGC -XX:+CMSParallelRemarkEnabled -XX:SurvivorRatio=8 -XX:MaxTenuringThreshold=10 -XX:CMSInitiatingOccupancyFraction=75 -XX:+UseCMSInitiatingOccupancyOnly -Djava.net.preferIPv4Stack=true -Dcom.sun.management.jmxremote.port=7199 -Dcom.sun.management.jmxremote.ssl=false -Dcom.sun.management.jmxremote.authenticate=false -Dmx4jport=8085 -Djava.rmi.server.hostname=10.210.101.106 -Dlog4j.configuration=log4j-server.properties -Dlog4j.defaultInitOverride=true -Dpasswd.properties=./../conf/passwd.properties -cp ./../conf:./../build/classes/main:./../build/classes/thrift:./../lib/antlr-3.2.jar:./../lib/apache-cassandra-0.8.6.jar:./../lib/apache-cassandra-thrift-0.8.6.jar:./../lib/avro-1.4.0-fixes.jar:./../lib/avro-1.4.0-sources-fixes.jar:./../lib/commons-cli-1.1.jar:./../lib/commons-codec-1.2.jar:./../lib/commons-collections-3.2.1.jar:./../lib/commons-lang-2.4.jar:./../lib/concurrentlinkedhashmap-lru-1.1.jar:./../lib/guava-r08.jar:./../lib/high-scale-lib-1.1.2.jar:./../lib/jackson-core-asl-1.4.0.jar:./../lib/jackson-mapper-asl-1.4.0.jar:./../lib/jamm-0.2.2.jar:./../lib/jline-0.9.94.jar:./../lib/jna.jar:./../lib/json-simple-1.1.jar:./../lib/libthrift-0.6.jar:./../lib/log4j-1.2.16.jar:./../lib/mx4j-tools.jar:./../lib/servlet-api-2.5-20081211.jar:./../lib/slf4j-api-1.6.1.jar:./../lib/slf4j-log4j12-1.6.1.jar:./../lib/snakeyaml-1.6.jar org.apache.cassandra.thrift.CassandraDaemon Top PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 2549 cassy 21 0 156g * 15g 11g *S 66.9 65.5 338:02.72 java Thank you in advance, Daning
