RelevantPortionofCassandra-env.sh

gistfile1.txt

if [ "$JVM_VERSION" \< "1.8.0" ] ; then
    ### Start CMS GC Settings
    # Used if Java version is not 1.8+, G1GC is used for Java 1.8+.

    # some JVMs will fill up their heap when accessed via JMX, see CASSANDRA-6541
    JVM_OPTS="$JVM_OPTS -XX:+CMSClassUnloadingEnabled"
    # CMS GC tuning options
    JVM_OPTS="$JVM_OPTS -Xmn${HEAP_NEWSIZE}"
    JVM_OPTS="$JVM_OPTS -XX:+UseParNewGC" 
    JVM_OPTS="$JVM_OPTS -XX:+UseConcMarkSweepGC" 
    JVM_OPTS="$JVM_OPTS -XX:+CMSParallelRemarkEnabled" 
    JVM_OPTS="$JVM_OPTS -XX:SurvivorRatio=8" 
    JVM_OPTS="$JVM_OPTS -XX:MaxTenuringThreshold=1"
    JVM_OPTS="$JVM_OPTS -XX:CMSInitiatingOccupancyFraction=75"
    JVM_OPTS="$JVM_OPTS -XX:+UseCMSInitiatingOccupancyOnly"
    JVM_OPTS="$JVM_OPTS -XX:CMSWaitDuration=10000"

    # note: bash evals '1.7.x' as > '1.7' so this is really a >= 1.7 jvm check
    if { [ "$JVM_VERSION" \> "1.7" ] && [ "$JVM_VERSION" \< "1.8.0" ] && [ "$JVM_PATCH_VERSION" -ge "60" ]; } || [ "$JVM_VERSION" \> "1.8" ] ; then
        JVM_OPTS="$JVM_OPTS -XX:+CMSParallelInitialMarkEnabled -XX:+CMSEdenChunksRecordAlways -XX:CMSWaitDuration=10000"
    fi

    if [ "$JVM_ARCH" = "64-Bit" ] ; then
        JVM_OPTS="$JVM_OPTS -XX:+UseCondCardMark"
    fi
    ### End CMS GC Settings
else # Java 1.8+
    ### Start G1GC Settings
    # Used when Java version is 1.8+
    # G1GC GC tuning options
    # Use the Hotspot garbage-first collector.
    JVM_OPTS="$JVM_OPTS -XX:+UseG1GC"

    # Have the JVM do less remembered set work during STW, instead
    # preferring concurrent GC. Reduces p99.9 latency.
    JVM_OPTS="$JVM_OPTS -XX:G1RSetUpdatingPauseTimePercent=5"

    # Main G1GC tunable: lowering the pause target will lower throughput and vise versa.
    # 200ms is the JVM default and lowest viable setting
    # 1000ms increases throughput. Keep it smaller than the timeouts in cassandra.yaml.
    JVM_OPTS="$JVM_OPTS -XX:MaxGCPauseMillis=500"

    # The JVM maximum is 8 PGC threads and 1/4 of that for ConcGC.
    # Machines with > 10 cores may need additional threads. Increase to <= full cores.
    #JVM_OPTS="$JVM_OPTS -XX:ParallelGCThreads=16"
    #JVM_OPTS="$JVM_OPTS -XX:ConcGCThreads=16"

    # Save CPU time on large (>= 16GB) heaps by delaying region scanning
    # until the heap is 70% full. The default in Hotspot 8u40 is 40%.
    #JVM_OPTS="$JVM_OPTS -XX:InitiatingHeapOccupancyPercent=70"

    ### End G1GC Settings
fi