• JVM调优命令-jmap

    jmap
    JVM Memory Map命令用于生成heap dump文件，如果不使用这个命令，还可以使用-XX:+HeapDumpOnOutOfMemoryError参数来让虚拟机出现OOM的时候自动生成dump文件。 jmap不仅能生成dump文件，还可以查询finalize执行队列、Java堆和永久代的详细信息，如当前使用率、当前使用的是哪种收集器等。【内存分析】
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    [root@localhost jdk1.7.0_79]# jmap --help
    Usage:
        jmap [option] <pid>
            (to connect to running process)
        jmap [option] <executable <core>
            (to connect to a core file)
        jmap [option] [server_id@]<remote server IP or hostname>
            (to connect to remote debug server)
     
    where <option> is one of:
        <none>               to print same info as Solaris pmap
        -heap                to print java heap summary
        -histo[:live]        to print histogram of java object heap; if the "live"
                             suboption is specified, only count live objects
        -permstat            to print permanent generation statistics
        -finalizerinfo       to print information on objects awaiting finalization
        -dump:<dump-options> to dump java heap in hprof binary format
                             dump-options:
                               live         dump only live objects; if not specified,
                                            all objects in the heap are dumped.
                               format=b     binary format
                               file=<file>  dump heap to <file>
                             Example: jmap -dump:live,format=b,file=heap.bin <pid>
        -F                   force. Use with -dump:<dump-options> <pid> or -histo
                             to force a heap dump or histogram when <pid> does not
                             respond. The "live" suboption is not supported
                             in this mode.
        -h | -help           to print this help message
        -J<flag>             to pass <flag> directly to the runtime system

    命令格式

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    jmap [ option ] pid
    jmap [ option ] executable core
    jmap [ option ] [server-id@]remote-hostname-or-IP
     

    参数

    option：选项参数，不可同时使用多个选项参数

    pid：java进程id，命令ps -ef | grep java获取

    executable：产生核心dump的java可执行文件

    core：需要打印配置信息的核心文件

    remote-hostname-or-ip：远程调试的主机名或ip

    server-id：可选的唯一id，如果相同的远程主机上运行了多台调试服务器，用此选项参数标识服务器

     

    options参数

    heap : 显示Java堆详细信息
    histo : 显示堆中对象的统计信息
    permstat :Java堆内存的永久保存区域的类加载器的统计信息
    finalizerinfo : 显示在F-Queue队列等待Finalizer线程执行finalizer方法的对象
    dump : 生成堆转储快照
    F : 当-dump没有响应时，强制生成dump快照

    示例

     

    -dump

    dump堆到文件,format指定输出格式，live指明是活着的对象,file指定文件名

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    [root@localhost jdk1.7.0_79]# jmap -dump:live,format=b,file=dump.hprof 24971
    Dumping heap to /usr/local/java/jdk1.7.0_79/dump.hprof ...
    Heap dump file created

    -heap

    打印heap的概要信息，GC使用的算法，heap的配置及使用情况，可以用此来判断内存目前的使用情况以及垃圾回收情况

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    [root@localhost jdk1.7.0_79]# jmap -heap 24971
    Attaching to process ID 24971, please wait...
    Debugger attached successfully.
    Server compiler detected.
    JVM version is 24.79-b02
     
    using thread-local object allocation.
    Parallel GC with 4 thread(s)
     
    Heap Configuration:
       MinHeapFreeRatio = 0
       MaxHeapFreeRatio = 100
       MaxHeapSize      = 4146069504 (3954.0MB)
       NewSize          = 1310720 (1.25MB)
       MaxNewSize       = 17592186044415 MB
       OldSize          = 5439488 (5.1875MB)
       NewRatio         = 2
       SurvivorRatio    = 8
       PermSize         = 21757952 (20.75MB)
       MaxPermSize      = 85983232 (82.0MB)
       G1HeapRegionSize = 0 (0.0MB)
     
    Heap Usage:
    PS Young Generation
    Eden Space:
       capacity = 517996544 (494.0MB)
       used     = 151567520 (144.54605102539062MB)
       free     = 366429024 (349.4539489746094MB)
       29.26033421566612% used
    From Space:
       capacity = 41943040 (40.0MB)
       used     = 0 (0.0MB)
       free     = 41943040 (40.0MB)
       0.0% used
    To Space:
       capacity = 40370176 (38.5MB)
       used     = 0 (0.0MB)
       free     = 40370176 (38.5MB)
       0.0% used
    PS Old Generation
       capacity = 115343360 (110.0MB)
       used     = 32927184 (31.401809692382812MB)
       free     = 82416176 (78.59819030761719MB)
       28.54709972034801% used
    PS Perm Generation
       capacity = 85983232 (82.0MB)
       used     = 54701200 (52.16712951660156MB)
       free     = 31282032 (29.832870483398438MB)
       63.6184506300019% used
     
    20822 interned Strings occupying 2441752 bytes.

    -finalizerinfo

    打印等待回收的对象信息，

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    [root@localhost jdk1.7.0_79]# jmap -finalizerinfo 24971
    Attaching to process ID 24971, please wait...
    Debugger attached successfully.
    Server compiler detected.
    JVM version is 24.79-b02
    Number of objects pending for finalization: 0

    Number of objects pending for finalization: 0 说明当前F-QUEUE队列中并没有等待Fializer线程执行final

    izer方法的对象。

     

    -histo

    打印堆的对象统计，包括对象数、内存大小等等。jmap -histo:live 这个命令执行，JVM会先触发gc，然后再统计信息

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    [root@localhost jdk1.7.0_79]# jmap -histo:live 24971 | more
     
     num     #instances         #bytes  class name
    ----------------------------------------------
       1:        100134       14622728  <constMethodKlass>
       2:        100134       12830128  <methodKlass>
       3:         88438       12708392  [C
       4:          8271       10163584  <constantPoolKlass>
       5:         27806        9115784  [B
       6:          8271        6225312  <instanceKlassKlass>
       7:          6830        5632192  <constantPoolCacheKlass>
       8:         86717        2081208  java.lang.String
       9:          2264        1311720  <methodDataKlass>
      10:         10880         870400  java.lang.reflect.Method
      11:          8987         869888  java.lang.Class
      12:         13330         747264  [[I
      13:         11808         733872  [S
      14:         20110         643520  java.util.concurrent.ConcurrentHashMap$HashEntry
      15:         18574         594368  java.util.HashMap$Entry
      16:          3668         504592  [Ljava.util.HashMap$Entry;
      17:         30698         491168  java.lang.Integer
      18:          2247         486864  [I
      19:          7486         479104  java.net.URL
      20:          8032         453616  [Ljava.lang.Object;
      21:         10259         410360  java.util.LinkedHashMap$Entry
      22:           699         380256  <objArrayKlassKlass>
      23:          5782         277536  org.apache.catalina.loader.ResourceEntry
      24:          8327         266464  java.lang.ref.WeakReference
      25:          2374         207928  [Ljava.util.concurrent.ConcurrentHashMap$HashEntry;
      26:          3440         192640  java.util.LinkedHashMap
      27:          4779         191160  java.lang.ref.SoftReference
      28:          3576         171648  java.util.HashMap
      29:         10080         161280  java.lang.Object

    jmap -histo:live 24971 | grep com.yuhuo 查询类名包含com.yuhuo的信息

    jmap -histo:live 24971 | grep com.yuhuo > histo.txt 保存信息到histo.txt文件

    附 - jmap输出中class name非自定义类的说明：

    BaseType CharacterTypeInterpretation
    B byte signed byte
    C char Unicode character
    D double double-precision floating-point value
    F float single-precision floating-point value
    I int integer
    J long long integer
    L; reference an instance of class
    S short signed short
    Z boolean true or false
    [ reference one array dimension，[I表示int[]

    -permstat

    打印Java堆内存的永久区的类加载器的智能统计信息。对于每个类加载器而言，它的名称、活跃度、地址、父类加载器、它所加载的类的数量和大小都会被打印。此外，包含的字符串数量和大小也会被打印。

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    [root@localhost jdk1.7.0_79]# jmap -permstat 24971
    Attaching to process ID 24971, please wait...
    Debugger attached successfully.
    Server compiler detected.
    JVM version is 24.79-b02
    finding class loader instances ..done.
    computing per loader stat ..done.
    please wait.. computing liveness....................................................liveness analysis may be inaccurate ...
    class_loader    classes bytes   parent_loader   alive?  type
     
    <bootstrap>   3034    18149440      null      live    <internal>
    0x000000070a88fbb8  1   3048      null      dead    sun/reflect/DelegatingClassLoader@0x0000000703c50b58
    0x000000070a914860  1   3064    0x0000000709035198  dead    sun/reflect/DelegatingClassLoader@0x0000000703c50b58
    0x000000070a9fc320  1   3056    0x0000000709035198  dead    sun/reflect/DelegatingClassLoader@0x0000000703c50b58
    0x000000070adcb4c8  1   3064    0x0000000709035198  dead    sun/reflect/DelegatingClassLoader@0x0000000703c50b58
    0x000000070a913760  1   1888    0x0000000709035198  dead    sun/reflect/DelegatingClassLoader@0x0000000703c50b58
    0x0000000709f3fd40  1   3032      null      dead    sun/reflect/DelegatingClassLoader@0x0000000703c50b58
    0x000000070923ba78  1   3088    0x0000000709035260  dead    sun/reflect/DelegatingClassLoader@0x0000000703c50b58
    0x000000070a88fff8  1   3048      null      dead    sun/reflect/DelegatingClassLoader@0x0000000703c50b58
    0x000000070adcbc58  1   1888    0x0000000709035198  dead    sun/reflect/DelegatingClassLoader@0x0000000703c50b58

    -F

    强制模式。如果指定的pid没有响应，请使用jmap -dump或jmap -histo选项。此模式下，不支持live子选项。
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  • 原文地址：https://www.cnblogs.com/AmilyWilly/p/8568779.html
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