JVM性能调优工具04-jcmd-Java程序诊断工具

[超级链接:JVM性能调优工具学习记录-序章]

本章主要学习Java程序诊断工具jcmd。

1.用途

发送诊断命令至正在活动的JVM。

2.语法

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1Usage: jcmd <pid | main class> <command ...|PerfCounter.print|-f file>

2   or: jcmd -l

3   or: jcmd -h

4

5  command must be a valid jcmd command for the selected jvm.

6  Use the command "help" to see which commands are available.

7  If the pid is 0, commands will be sent to all Java processes.

8  The main class argument will be used to match (either partially

9  or fully) the class used to start Java.

10  If no options are given, lists Java processes (same as -p).

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12  PerfCounter.print display the counters exposed by this process

13  -f  read and execute commands from the file

14  -l  list JVM processes on the local machine

15  -h  this help

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• h：帮助。

• l：显示当前机器上的进程，包括进程id、主类全路径名、main方法参数，等同于jps -ml。

• f：从文件读取并执行命令。

• PerfCounter.print：打印性能计数器信息。

• help：显示当前JVM进程可用的命令。

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1C:\Users\hanchao>jcmd 7484 help

27484:

3The following commands are available:

4JFR.stop

5JFR.start

6JFR.dump

7JFR.check

8VM.native_memory

9VM.check_commercial_features

10VM.unlock_commercial_features

11ManagementAgent.stop

12ManagementAgent.start_local

13ManagementAgent.start

14GC.rotate_log

15Thread.print

16GC.class_stats

17GC.class_histogram

18GC.heap_dump

19GC.run_finalization

20GC.run

21VM.uptime

22VM.flags

23VM.system_properties

24VM.command_line

25VM.version

26help

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3.常用命令示例

• jcmd pid VM.uptime:VM启动时间

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1C:\Users\hanchao>jcmd 7484 VM.uptime

27484:

35783.212 s

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• jcmd pid VM.system_properties:VM系统属性

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1C:\Users\hanchao>jcmd 7484 VM.system_properties

27484:

3#Tue May 08 23:22:22 CST 2018

4java.runtime.name=Java(TM) SE Runtime Environment

5sun.boot.library.path=C\:\\Program Files\\Java\\jdk1.8.0_131\\jre\\bin

6java.vm.version=25.131-b11

7java.vm.vendor=Oracle Corporation

8java.vendor.url=http\://java.oracle.com/

9...

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• jcmd pid Thread.print打印线程信息

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1C:\Users\hanchao>jcmd 7484 Thread.print

27484:

32018-05-08 23:23:13

4Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.131-b11 mixed mode):

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6"DestroyJavaVM" #13 prio=5 os_prio=0 tid=0x00000000047a3800 nid=0x3a8 waiting on condition [0x0000000000000000]

7   java.lang.Thread.State: RUNNABLE

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9"Thread-1" #12 prio=5 os_prio=0 tid=0x000000001ab7b800 nid=0xe64 waiting on condition [0x000000001bd7f000]

10   java.lang.Thread.State: TIMED_WAITING (sleeping)

11        at java.lang.Thread.sleep(Native Method)

12        at pers.hanchao.concurrent.eg04.ThreadWaitDemo$Restaurant.run(ThreadWaitDemo.java:105)

13        - locked <0x00000000d63bfd00> (a java.util.LinkedList)

14...

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• jcmd pid GC.class_histgram:类统计信息，包括类名、实例个数、内存大小等。

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1C:\Users\hanchao>jcmd 7484 GC.class_histogram

27484:

3

4 num     #instances         #bytes  class name

5----------------------------------------------

6   1:          6510         558304  [C

7   2:           716         458368  [B

8   3:          6365         152760  java.lang.String

9   4:           991         113016  java.lang.Class

10   5:           810          56856  [Ljava.lang.Object;

11   6:           835          33400  java.util.TreeMap$Entry

12   7:           817          26144  java.util.HashMap$Node

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• jcmd pid VM.flgs:获取启动参数

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1C:\Users\hanchao>jcmd 7484 VM.flags

27484:

3-XX:CICompilerCount=3 -XX:InitialHeapSize=134217728 -XX:MaxHeapSize=2126512128 -XX:MaxNewSize=708837376 -XX:MinHeapDeltaBytes=524288 -XX:NewSize=44564480 -XX:OldSize=89653248 -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseFastUnorderedTimeStamps -XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGC

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• jcmd pid GC.heap_dump dump.bin：将堆信息导入到项目根目录下的dump.bin文件中，以供其他分析工具进行分析。

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1C:\Users\hanchao>jcmd 7484 GC.heap_dump dump.bin

27484:

3Heap dump file created

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• jcmd pid PerfCounter.print:获取性能相关参数。