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java 15:用jmap查看堆内存相关信息

JAVA内存 查看 信息 相关 15
2023-09-14 09:01:18 时间

一，jmap查看帮助：

[lhdop@blog ~]$ jmap --help
Usage:
    jmap -clstats <pid>
        to connect to running process and print class loader statistics
    jmap -finalizerinfo <pid>
        to connect to running process and print information on objects awaiting finalization
    jmap -histo[:[<histo-options>]] <pid>
        to connect to running process and print histogram of java object heap
    jmap -dump:<dump-options> <pid>
        to connect to running process and dump java heap
    jmap -? -h --help
        to print this help message
 
    dump-options:
      live         dump only live objects
      all          dump all objects in the heap (default if one of "live" or "all" is not specified
      format=b     binary format
      file=<file>  dump heap to <file>
 
    Example: jmap -dump:live,format=b,file=heap.bin <pid>
 
    histo-options:
      live         count only live objects
      all          count all objects in the heap (default if one of "live" or "all" is not specified)
      file=<file>  dump data to <file>
 
    Example: jmap -histo:live,file=/tmp/histo.data <pid>

说明：刘宏缔的架构森林是一个专注架构的博客，地址：https://www.cnblogs.com/architectforest

         对应的源码可以访问这里获取： https://github.com/liuhongdi/
         或: https://gitee.com/liuhongdi

说明：作者:刘宏缔 邮箱: 371125307@qq.com

二，jmap的常用例子

1,显示堆中对象的统计信息
[lhdop@blog ~]$ jmap -histo:live 5426 | more
No dump file specified
num     #instances         #bytes  class name (module)
-------------------------------------------------------
   1:        262144        6291456  org.apache.logging.log4j.core.async.AsyncLoggerConfigDisruptor$Log4jEventWrapper
   2:         77084        5499016  [B (java.base@15)
   3:          5678        4699536  [I (java.base@15)
   4:         72731        1745544  java.lang.String (java.base@15)
   5:         11294        1692816  [Ljava.lang.Object; (java.base@15)
   6:         48063        1538016  java.util.concurrent.ConcurrentHashMap$Node (java.base@15)
   7:         12598        1501528  java.lang.Class (java.base@15)
   8:         15105        1329240  java.lang.reflect.Method (java.base@15)
   9:           547         902144  [C (java.base@15)
  10:         18089         578848  java.util.HashMap$Node (java.base@15)
  11:          5975         530328  [Ljava.util.HashMap$Node; (java.base@15)
  12:         12632         505280  java.util.LinkedHashMap$Entry (java.base@15)
  13:           445         482320  [Ljava.util.concurrent.ConcurrentHashMap$Node; (java.base@15)
  14:         25730         411680  java.lang.Object (java.base@15)
  15:          6481         362936  java.util.LinkedHashMap (java.base@15)
  16:         11761         266568  [Ljava.lang.Class; (java.base@15)
...
2,打印类加载器信息
[lhdop@blog ~]$ jmap -clstats 5426
ClassLoader         Parent              CLD*               Classes   ChunkSz   BlockSz  Type
0x00000008000a6190  0x0000000800b98840  0x00007f86240485a0       1      3072      2024  jdk.internal.reflect.DelegatingClassLoader
0x00000008000a6190  0x0000000800b98840  0x00007f8638279130       1      6144      4032  jdk.internal.reflect.DelegatingClassLoader
0x00000008000a6190  0x000000080007f230  0x00007f8628201320       1      4096      3232  jdk.internal.reflect.DelegatingClassLoader
0x00000008000a6190  0x0000000800b98840  0x00007f86b94f11a0       1      6144      3968  jdk.internal.reflect.DelegatingClassLoader
0x00000008000a6190  0x0000000800b98840  0x0000565402b9e740       1      3072      2024  jdk.internal.reflect.DelegatingClassLoader
0x00000008000a6190  0x000000080007f230  0x00007f8648278e70       1      6144      4784  jdk.internal.reflect.DelegatingClassLoader
0x00000008000a6190  0x0000000800b98840  0x00007f863000a560       1      6144      4056  jdk.internal.reflect.DelegatingClassLoader
…
Total = 456                                                  12549  65325056  64231288
ChunkSz: Total size of all allocated metaspace chunks
BlockSz: Total size of all allocated metaspace blocks (each chunk has several blocks)
3,打印等待终结的对象信息
[lhdop@blog ~]$ jmap -finalizerinfo 5426
No instances waiting for finalization found
4,以hprof二进制格式转储Java堆到指定filename的文件中
[lhdop@blog ~]$ jmap -dump:live,format=b,file=heap.hprof 5426
Dumping heap to /home/lhdop/heap.hprof ...
Heap dump file created [60868455 bytes in 0.264 secs]
查看生成的二进制文件:
[lhdop@blog ~]$ ll heap.hprof
-rw------- 1 lhdop lhdop 60868455 Mar 26 17:08 heap.hprof
说明：
dump的文件可以使用eclipse的MAT或jdk自带的jvisualvm分析内存泄露和内存溢出问题。
 

三，查看java版本:

[lhdop@blog tools]$ java --version
java 15 2020-09-15
Java(TM) SE Runtime Environment (build 15+36-1562)
Java HotSpot(TM) 64-Bit Server VM (build 15+36-1562, mixed mode, sharing)

 

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