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

1 2	# 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

1 2	#1s show jstat -gc -t <<pid>> 1000

output

 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:

参考Oracle GC Doc

jcmd

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

heap dump dump 进程的heap.

# 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.

# 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

参照 jstat命令查看jvm的GC情况

JVM jstat jcmd command

jstat 简介

jstat 常用命令

jstat gc

jcmd

其它几个命令使用

参考