JVM jstat jcmd command

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jstat 简介

jstat - Java Virtual Machine Statistics Monitoring Tool.The jstat utility uses the built-in instrumentation in the Java HotSpot VM to provide information about performance and resource consumption of running applications. Oracle docs

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# show options 
jstat -options

jstat option list:

Option Displays...
class Statistics on the behavior of the class loader.
compiler Statistics of the behavior of the HotSpot Just-in-Time compiler.
gc Statistics of the behavior of the garbage collected heap.
gccapacity Statistics of the capacities of the generations and their corresponding spaces.
gccause

Summary of garbage collection statistics (same as -gcutil), with the cause of the last and current (if applicable) garbage collection events.

gcnew Statistics of the behavior of the new generation.
gcnewcapacity Statistics of the sizes of the new generations and its corresponding spaces.
gcold Statistics of the behavior of the old and permanent generations.
gcoldcapacity Statistics of the sizes of the old generation.
gcpermcapacity Statistics of the sizes of the permanent generation.
gcutil Summary of garbage collection statistics.
printcompilation HotSpot compilation method statistics.

jstat 常用命令

jstat gc

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#1s show 
jstat -gc -t <<pid>> 1000

output 

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 S0C    S1C    S0U    S1U      EC       EU        OC         OU       MC     MU    CCSC   CCSU   YGC     YGCT    FGC    FGCT     GCT
209664.0 209664.0  0.0   37198.6 1677824.0 1144385.2 2097152.0   163729.1  111116.0 106844.1 12444.0 11713.9     19    1.142   4      1.131    2.273
209664.0 209664.0  0.0   37198.6 1677824.0 1144385.2 2097152.0   163729.1  111116.0 106844.1 12444.0 11713.9     19    1.142   4      1.131    2.273
209664.0 209664.0  0.0   37198.6 1677824.0 1144538.5 2097152.0   163729.1  111116.0 106844.1 12444.0 11713.9     19    1.142   4      1.131    2.273
209664.0 209664.0  0.0   37198.6 1677824.0 1184081.7 2097152.0   163729.1  111116.0 106844.1 12444.0 11713.9     19    1.142   4      1.131    2.273
209664.0 209664.0  0.0   37198.6 1677824.0 1207177.7 2097152.0   163729.1  111116.0 106844.1 12444.0 11713.9     19    1.142   4      1.131    2.273
209664.0 209664.0  0.0   37198.6 1677824.0 1207488.4 2097152.0   163729.1  111116.0 106844.1 12444.0 11713.9     19    1.142   4      1.131    2.273

GC 指标 info Desc..
S0C Current survivor space 0 capacity (kB).
S1C Current survivor space 1 capacity (kB).
S0U Survivor space 0 utilization (kB).
S1U Survivor space 1 utilization (kB).
EC Current eden space capacity (kB).
EU Eden space utilization (kB).
OC Current old space capacity (kB).
OU Old space utilization (kB).
MC Metaspace capacity (kB).
MU Metacspace utilization (kB).
CCSC Compressed class space capacity (kB).
CCSU Compressed class space used (kB).
YGC Number of young generation garbage collection events.
YGCT Young generation garbage collection time.
FGC Number of full GC events.
FGCT Full garbage collection time.
GCT Total garbage collection time.

为便于理解输出的指标,先理解一下CMS/ G1GC Heap结构,简单介绍一下C1/CMS Heap Structure:

G1 Collector:

CMS/serial/parallel Collector:

jcmd

jcmd用于向JVM发送diagnostic command （JDK8及以上）.

  • heap dump dump 进程的heap.
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    # jcmd 7891 GC.heap_dump filename=./7891_gc_dump.dump
    $ jcmd <JAVA_PID> GC.heap_dump filename=<FILE>

    #通过浏览器查看 dump文件 http://hostname:7000
    # jhat ./7891_gc_dump.hbin
  • VM classload java 进程启动的信息
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    # java 进程启动信息
    # VM.flags 可以查看设置的参数
    $ jcmd 17995 VM.command_line
  • Troubleshoot with jcmd Utility 使用jcmd启动、停止Troubleshoot Tool.
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    # 强制 对进程执行GC
    $ jcmd  $PID  GC.run

    # 启动/停止 ManagementAgent 
    # 可以使用JMXAgent 工具JConsole 观察JVM运行状况和运行的参数（GC、Heap信息）
    $ jcmd $PID ManagementAgent.start jmxremote.port=10333 jmxremote.authenticate=false jmxremote.ssl=false

    # agent stop
    $ jcmd  $PID  ManagementAgent.stop

其它几个命令使用

参考