JVM性能调优工具05-jmap和jhat-JVM对象内存监测工具

[超级链接:JVM性能调优工具学习记录-序章]

本章主要学习JVM对象内存监测工具jmap和jhat。

1.用途

jmap：打印JVM中对象的统计信息，包括内存占用、实例个数、对象类型等。

jhat：对Heap进行离线分析，并以Html页面显示结果的工具。

2.jmap用法

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1Usage:

2    jmap [option] <pid>

3        (to connect to running process)

4    jmap [option] <executable <core>

5        (to connect to a core file)

6    jmap [option] [server_id@]<remote server IP or hostname>

7        (to connect to remote debug server)

8

9where <option> is one of:

10    <none>               to print same info as Solaris pmap

11    -heap                to print java heap summary

12    -histo[:live]        to print histogram of java object heap; if the "live"

13                         suboption is specified, only count live objects

14    -clstats             to print class loader statistics

15    -finalizerinfo       to print information on objects awaiting finalization

16    -dump:<dump-options> to dump java heap in hprof binary format

17                         dump-options:

18                           live         dump only live objects; if not specified,

19                                        all objects in the heap are dumped.

20                           format=b     binary format

21                           file=<file>  dump heap to <file>

22                         Example: jmap -dump:live,format=b,file=heap.bin <pid>

23    -F                   force. Use with -dump:<dump-options> <pid> or -histo

24                         to force a heap dump or histogram when <pid> does not

25                         respond. The "live" suboption is not supported

26                         in this mode.

27    -h | -help           to print this help message

28    -J<flag>             to pass <flag> directly to the runtime system

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• J<flag>：设置JVM参数。

• h | help：帮助。

• F：在pid的情况下强制使用-dump或者-histo参数. 在这个模式下,live子参数无效.

• heap：打印堆统计信息。

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1C:\Users\hanchao>jmap -heap 7484

2Attaching to process ID 7484, please wait...

3Debugger attached successfully.

4Server compiler detected.

5JVM version is 25.131-b11

6

7using thread-local object allocation.

8Parallel GC with 4 thread(s)

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10Heap Configuration:

11   MinHeapFreeRatio         = 0

12   MaxHeapFreeRatio         = 100

13   MaxHeapSize              = 2126512128 (2028.0MB)

14   NewSize                  = 44564480 (42.5MB)

15   MaxNewSize               = 708837376 (676.0MB)

16   OldSize                  = 89653248 (85.5MB)

17...

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• histo：打印堆中的Java对象直方图，包括：序号、实例个数、内存大小、类名。

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1C:\Users\hanchao>jmap -histo 7484

2

3 num     #instances         #bytes  class name

4----------------------------------------------

5   1:           308        1063632  [I

6   2:         11594        1036064  [C

7   3:          8319         199656  java.lang.String

8   4:          3508         177080  [Ljava.lang.String;

9   5:           448         150152  [B

10   6:           991         113016  java.lang.Class

11   7:          1326          65112  [Ljava.lang.Object;

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• histo:live：与histo类似，只不过只打印存活的对象。

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1C:\Users\hanchao>jmap -histo:live 7484

2

3 num     #instances         #bytes  class name

4----------------------------------------------

5   1:          6510         556792  [C

6   2:          6365         152760  java.lang.String

7   3:           447         150048  [B

8   4:           991         113016  java.lang.Class

9   5:           810          56856  [Ljava.lang.Object;

10   6:           835          33400  java.util.TreeMap$Entry

11   7:           817          26144  java.util.HashMap$Node

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• clstats：打印ClassLoader统计信息。

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1C:\Users\hanchao>jmap -clstats 7484

2Attaching to process ID 7484, please wait...

3Debugger attached successfully.

4Server compiler detected.

5JVM version is 25.131-b11

6finding class loader instances ..done.

7computing per loader stat ..done.

8please wait.. computing liveness............liveness analysis may be inaccurate ...

9class_loader    classes bytes   parent_loader   alive?  type

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11<bootstrap>     807     1472448   null          live    <internal>

120x0000000081402ef0      141     323773  0x0000000081402f50      live    sun/misc/Launcher$AppClassLoader@0x000000010000f6a0

130x0000000081402f50      8       15664     null          live    sun/misc/Launcher$ExtClassLoader@0x000000010000fa48

140x00000000814d0ac0      0       0       0x0000000081402ef0      dead    java/util/ResourceBundle$RBClassLoader@0x00000001000875f0

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16total = 4       956     1811885     N/A         alive=3, dead=1     N/A

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• finalizerinfo：打印等待回收的对象信息。

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1C:\Users\hanchao>jmap -finalizerinfo 7484

2Attaching to process ID 7484, please wait...

3Debugger attached successfully.

4Server compiler detected.

5JVM version is 25.131-b11

6Number of objects pending for finalization: 0

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• dump:live,format=b,file=dump.bin：导出堆信息，要求只导出存活的对象，以二进制格式，导出文件名为dump.bin。

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1C:\Users\hanchao>jmap -dump:live,format=b,file=dump2018.bin 7484

2Dumping heap to C:\Users\hanchao\dump2018.bin ...

3Heap dump file created

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3.分析过程

1. 通过jmap或jcmd导出heap dump至文件dump.bin。

通过jhat dump.bin分析文件。

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1C:\Users\hanchao>jhat dump.bin

2Reading from dump.bin...

3Dump file created Sun May 06 23:39:09 CST 2018

4Snapshot read, resolving...

5Resolving 175671 objects...

6Chasing references, expect 35 dots...................................

7Eliminating duplicate references...................................

8Snapshot resolved.

9Started HTTP server on port 7000

10Server is ready.

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1. 在浏览器访问http://localhost:7000/看分析结果。