jmap 使用--jvm 虚拟机

朱雀 2023-10-18 12:01 25阅读 0赞

## **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】

### **命令格式** ###

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

### **-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。

[root@xx254203 ~]# jmap -heap 1341
    Attaching to process ID 1341, please wait...
    Debugger attached successfully.
    Server compiler detected.
    JVM version is 25.181-b13
    
    using thread-local object allocation.
    Mark Sweep Compact GC
    
    Heap Configuration:
       MinHeapFreeRatio         = 40   //对应jvm启动参数-XX:MinHeapFreeRatio设置JVM堆最小空闲比率(default 40)
       MaxHeapFreeRatio         = 70//对应jvm启动参数 -XX:MaxHeapFreeRatio设置JVM堆最大空闲比率(default 70)
       MaxHeapSize              = 132120576 (126.0MB) //对应jvm启动参数-XX:MaxHeapSize=设置JVM堆的最大大小
       NewSize                  = 2752512 (2.625MB)  //对应jvm启动参数-XX:NewSize=设置JVM堆的‘新生代’的默认大小
       MaxNewSize               = 44040192 (42.0MB)  //对应jvm启动参数-XX:MaxNewSize=设置JVM堆的‘新生代’的最大大小
       OldSize                  = 5636096 (5.375MB)  //对应jvm启动参数-XX:OldSize=<value>:设置JVM堆的‘老生代’的大小
       NewRatio                 = 2  //对应jvm启动参数-XX:NewRatio=:‘新生代’和‘老生代’的大小比率
       SurvivorRatio            = 8  //对应jvm启动参数-XX:SurvivorRatio=设置年轻代中Eden区与Survivor区的大小比值
       MetaspaceSize            = 21807104 (20.796875MB) //元空间大小
       CompressedClassSpaceSize = 1073741824 (1024.0MB)  //压缩类空间大小
       MaxMetaspaceSize         = 17592186044415 MB      //最大元空间大小
       G1HeapRegionSize         = 0 (0.0MB)        
       //Region是实现G1算法的基础,每个Region的大小相等,通过-XX:G1HeapRegionSize参数可以设置Region的大小
    
    Heap Usage: //堆内存分步
    New Generation (Eden + 1 Survivor Space):
       capacity = 7667712 (7.3125MB)
       used     = 3396264 (3.2389297485351562MB)
       free     = 4271448 (4.073570251464844MB)
       44.29305639022436% used
    Eden Space://Eden区内存分布
       capacity = 6881280 (6.5625MB)           //Eden区总容量
       used     = 3387328 (3.23040771484375MB) //Eden区已使用
       free     = 3493952 (3.33209228515625MB) //Eden区剩余容量
       49.225260416666664% used                //Eden区使用比率
    From Space://其中一个Survivor区的内存分布
       capacity = 786432 (0.75MB)
       used     = 8936 (0.00852203369140625MB)
       free     = 777496 (0.7414779663085938MB)
       1.1362711588541667% used
    To Space:  //另一个Survivor区的内存分布
       capacity = 786432 (0.75MB)
       used     = 0 (0.0MB)
       free     = 786432 (0.75MB)
       0.0% used
    tenured generation://老年代
       capacity = 16805888 (16.02734375MB)
       used     = 13239288 (12.625968933105469MB)
       free     = 3566600 (3.4013748168945312MB)
       78.77767601450158% used
    
    11998 interned Strings occupying 1724416 bytes.

### **-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

[root@xx254203 ~]# jmap -dump:live,format=b,file=/tmp/dump.hprof 1341
    Dumping heap to /tmp/dump.hprof ...
    Heap dump file created

### **-finalizerinfo** ###

打印等待回收的对象信息

[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finalizer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

[root@xx254203 ~]# jmap -histo:live 1341 |more
    
     num     #instances         #bytes  class name
    ----------------------------------------------
       1:         30901        5811600  [C
       2:         29765         714360  java.lang.String
       3:         14864         475648  java.util.HashMap$Node
       4:          4518         397584  java.lang.reflect.Method
       5:          3001         340728  java.lang.Class
       6:           795         316000  [B
       7:          3530         206144  [Ljava.lang.Object;
       8:           958         171184  [Ljava.util.HashMap$Node;
       9:          4740         151680  java.util.concurrent.ConcurrentHashMap$Node
      10:          1666          84176  [I
      11:          1563          75024  java.util.HashMap
      12:           820          63488  [Ljava.lang.String;
      13:          3968          63488  java.lang.Object
      14:          1247          49880  java.util.LinkedHashMap$Entry
      15:          2451          49576  [Ljava.lang.Class;
      16:          1434          45888  java.util.Hashtable$Entry
      17:          1027          41080  java.util.TreeMap$Entry
      18:           817          39216  org.apache.tomcat.util.modeler.AttributeInfo
      19:           482          38560  java.lang.reflect.Constructor
      20:            76          37152  [Ljava.util.concurrent.ConcurrentHashMap$Node;
      21:           133          33672  [[C
      22:           789          31560  java.lang.ref.SoftReference
     。。。。。。。

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：**

<table> 
 <thead> 
  <tr> 
   <th>BaseType&nbsp;Character</th> 
   <th>Type</th> 
   <th>Interpretation</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>B</td> 
   <td>byte</td> 
   <td>signed&nbsp;byte</td> 
  </tr> 
  <tr> 
   <td>C</td> 
   <td>char</td> 
   <td>Unicode&nbsp;character</td> 
  </tr> 
  <tr> 
   <td>D</td> 
   <td>double</td> 
   <td>double-precision&nbsp;floating-point&nbsp;value</td> 
  </tr> 
  <tr> 
   <td>F</td> 
   <td>float</td> 
   <td>single-precision&nbsp;floating-point&nbsp;value</td> 
  </tr> 
  <tr> 
   <td>I</td> 
   <td>int</td> 
   <td>integer</td> 
  </tr> 
  <tr> 
   <td>J</td> 
   <td>long</td> 
   <td>long&nbsp;integer</td> 
  </tr> 
  <tr> 
   <td>L;</td> 
   <td>reference</td> 
   <td>an&nbsp;instance&nbsp;of&nbsp;class</td> 
  </tr> 
  <tr> 
   <td>S</td> 
   <td>short</td> 
   <td>signed&nbsp;short</td> 
  </tr> 
  <tr> 
   <td>Z</td> 
   <td>boolean</td> 
   <td>true&nbsp;or&nbsp;false</td> 
  </tr> 
  <tr> 
   <td>[</td> 
   <td>reference</td> 
   <td>one&nbsp;array&nbsp;dimension，[I表示int[]</td> 
  </tr> 
 </tbody> 
</table>

### **-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。

### [\-*clstats* ][-_clstats_] ###

Java堆中内存的类加载器的统计信息

[root@xx254203 ~]# jmap -clstats 1341
    Attaching to process ID 1341, please wait...
    Debugger attached successfully.
    Server compiler detected.
    JVM version is 25.181-b13
    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>     2002    3420852   null          live    <internal>
    0x00000000fad3c310      1       1473    0x00000000fac78820      dead    sun/reflect/DelegatingClassLoader@0x000000010000a028
    0x00000000fad3c950      1       1473    0x00000000fac78820      dead    sun/reflect/DelegatingClassLoader@0x000000010000a028
    0x00000000fb430000      1       1473    0x00000000fac78820      dead  sun/reflect/DelegatingClassLoader@0x000000010000a028
    0x00000000fac78970      35      56572   0x00000000fac96cc0      live    sun/misc/Launcher$AppClassLoader@0x000000010000f8d0
    0x00000000fad7cb20      1       1476    0x00000000fac78820      dead    sun/reflect/DelegatingClassLoader@0x000000010000a028
    0x00000000fad3c568      1       1473    0x00000000fac78820      dead    sun/reflect/DelegatingClassLoader@0x000000010000a028
    0x00000000fb539228      0       0       0x00000000fac78820      live    org/apache/catalina/loader/ParallelWebappClassLoader@0x00000001001731e8
    0x00000000fb4d37f0      1       1473    0x00000000fac78820      dead    sun/reflect/DelegatingClassLoader@0x000000010000a028
    0x00000000fb4d3e30      1       1476    0x00000000fac78820      dead    sun/reflect/DelegatingClassLoader@0x000000010000a028
    
    total = 44      2723    4801535     N/A         alive=10, dead=34           N/A

### **-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。

[-_clstats_]: http://www.baidu.com/link?url=1vNZMtMwMLWb7iTyxx57G6boxvVDcESJRSoKxF1gSwPip310C4rnWlreTfSZeXLloKpDC4g6TySO-eZct16eEp4MAb3GoTs9sw0NlfQROeu