JVM Optimize

  • print JVM config :-XX
    java -XX:+PrintCommandLineFlags -version

    It will show message:


-XX:InitialHeapSize=129263744 -XX:MaxHeapSize=2068219904 -XX:+PrintCommandLineFl
ags -XX:+UseCompressedOops -XX:-UseLargePagesIndividualAllocation -XX:+UseParall
elGC
java version "1.7.0_99"
Java(TM) SE Runtime Environment (build 1.7.0_99-b04)
Java HotSpot(TM) 64-Bit Server VM (build 24.95-b01, mixed mode)

  • config heap
    java -Xmx3550m -Xms3550m -Xss128k -XX:NewRatio=4 -XX:SurvivorRatio=4 -XX:MaxPermSize=16m -XX:MaxTenuringThreshold=0
    1)-Xmx: set JVM maxsize

    2)-Xms: set JVM initial size

    3)-Xmn: set young size

    4)-Xss: set heap size for thread

    5)-XX:NewRatio=4:set value=young size(Eden+2 Survivor):old size.Young accounts for 1/5 of heap

    6)-XX:SurvivorRatio=4:set value=Eden:SurvivorRatio.SurvivorRatio accounts for 1/6 of young

    7)-XX:MaxPermSize=16m:set perm max size

    8)-XX:MaxTenuringThreshold:set max surviving period of garbage
    ①if -XX:MaxTenuringThreshold=0
    Young generation of objects without Survivor area, directly into the old generation
    It can improve efficiency for the older generation of more applications
    ②if -XX:MaxTenuringThreshold with large value
    The younger generation of objects in the Survivor area will be repeated many times, which can increase the survival of the younger generation of the object.

  • Recycling option
    Parallel collector is mainly aimed at reaching a certain throughput
    1)Configuring parallel collectors for younger generation
    java -Xmx3800m -Xms3800m -Xmn2g -Xss128k -XX:+UseParallelGC -XX:ParallelGCThreads=20

    -XX:+UseParallelGC:Select parallel collector for young
    -XX:ParallelGCThreads:Set number of threads in parallel collector

    2)Configuring parallel collectors for old generation
    java -XX:+UseParallelOldGC
    -XX:+UseParallelOldGC:Select parallel collector for old

    3)config max time of young garbage collection

    java -Xmx3550m -Xms3550m -Xmn2g -Xss128k -XX:+UseParallelGC -XX:MaxGCPauseMillis=100
    -XX:MaxGCPauseMillis=100:
    If this time is not met, JVM automatically adjusts the young generation size to meet this value

    Concurrent collector is mainly to ensure the response time of the system and reduce the time of garbage collection
    1)Set concurrent collection for old
    java -XX:+UseConcMarkSweepGC -Xmn2g
    -XX:NewRatio will become invalid.

    2)Memory space for compression, sorting

    java -Xmx3550m -Xms3550m -Xmn2g -Xss128k -XX:+UseConcMarkSweepGC -XX:CMSFullGCsBeforeCompaction=5 -XX:+UseCMSCompactAtFullCollection -XX:CMSFullGCsBeforeCompaction: Compress and organize memory space after finish GC run time -XX:+UseCMSCompactAtFullCollection: Open the compression of the old generation

  • summary
    1)young
    ①response time prior as large as limit
    The frequency of young generation collection is the smallest. It help to reduce the arrival of the older generation of objects

    ②throughput prior
    as large as limit.It adapt to ≥8CPU

    2)old
    ①response time prior
    It need to refence:
    Concurrent garbage collection information
    Collection times of persistent generation
    Traditional GC information
    The proportion of time spent on the recovery of young and old generations

    ②throughput prior
    large young + small old