JVM性能优化详解
JVM相关工具
$JAVA_HOME/bin下
| 命令 | 说明 |
|---|---|
| jps | 查看所有jvm进程 |
| jinfo | 查看进程的运行环境参数，主要是jvm命令行参数 |
| jstat | 对jvm应用程序的资源和性能进行实时监控 |
| jstack | 查看所有线程的运行状态 |
| jmap | 查看jvm占用物理内存的状态 |
| jhat | +UseParNew |
| jconsole | |
| jvisualvm |
jps：Java virutal machine Process Status tool，
jps [-q] [-mlvV] [<hostid>]
-q：静默模式；
-v：显示传递给jvm的命令行参数；
-m：输出传入main方法的参数；
-l：输出main类或jar完全限定名称；
-v：显示通过flag文件传递给jvm的参数；
[<hostid>]：主机id，默认为localhost；
详细列出当前Java进程信息
[root@tomcat ~]#jps -l -v
21560 org.netbeans.Main -Djdk.home=/usr/local/jdk -Dnetbeans.default_userdir_root=/root/.visualvm -Dnetbeans.dirs=/usr/local/jdk/lib/visualvm/visualvm:/usr/local/jdk/lib/visualvm/profiler: -Dnetbeans.home=/usr/local/jdk/lib/visualvm/platform -Xms24m -Xmx256m -Dsun.jvmstat.perdata.syncWaitMs=10000 -Dsun.java2d.noddraw=true -Dsun.java2d.d3d=false -Dnetbeans.keyring.no.master=true -Dplugin.manager.install.global=false --add-exports=java.desktop/sun.awt=ALL-UNNAMED --add-exports=jdk.jvmstat/sun.jvmstat.monitor.event=ALL-UNNAMED --add-exports=jdk.jvmstat/sun.jvmstat.monitor=ALL-UNNAMED --add-exports=java.desktop/sun.swing=ALL-UNNAMED --add-exports=jdk.attach/sun.tools.attach=ALL-UNNAMED --add-modules=java.activation -XX:+IgnoreUnrecognizedVMOptions -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/root/.visualvm/8u131/var/log/heapdump.hprof
22270 sun.tools.jps.Jps -Denv.class.path=/usr/local/jdk/lib/:/usr/local/jdk/jre/lib/ -Dapplication.home=/usr/local/jdk1.8.0_241 -Xms8m
21407 HelloWorld -Xms256m -Xmx512m
jinfo：输出给定的java进程的所有配置信息；
jinfo [option] <pid>
-flags：打印 VM flags
-sysprops：to print Java system properties
-flag <name>：to print the value of the named VM flag
先获得一个java进程ID，然后jinfo
[root@tomcat ~]#jps
22357 Jps
21560 Main
21407 HelloWorld
[root@tomcat ~]#jinfo 21407
Attaching to process ID 21407, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.241-b07
Java System Properties:
java.runtime.name = Java(TM) SE Runtime Environment
java.vm.version = 25.241-b07
sun.boot.library.path = /usr/local/jdk1.8.0_241/jre/lib/amd64
java.vendor.url = http://java.oracle.com/
java.vm.vendor = Oracle Corporation
path.separator = :
java.rmi.server.randomIDs = true
file.encoding.pkg = sun.io
java.vm.name = Java HotSpot(TM) 64-Bit Server VM
sun.os.patch.level = unknown
sun.java.launcher = SUN_STANDARD
user.country = US
user.dir = /data
java.vm.specification.name = Java Virtual Machine Specification
java.runtime.version = 1.8.0_241-b07
java.awt.graphicsenv = sun.awt.X11GraphicsEnvironment
os.arch = amd64
java.endorsed.dirs = /usr/local/jdk1.8.0_241/jre/lib/endorsed
java.io.tmpdir = /tmp
line.separator =
java.vm.specification.vendor = Oracle Corporation
os.name = Linux
sun.jnu.encoding = UTF-8
java.library.path = /usr/java/packages/lib/amd64:/usr/lib64:/lib64:/lib:/usr/lib
java.specification.name = Java Platform API Specification
java.class.version = 52.0
sun.management.compiler = HotSpot 64-Bit Tiered Compilers
os.version = 4.18.0-147.el8.x86_64
user.home = /root
user.timezone = Asia/Shanghai
java.awt.printerjob = sun.print.PSPrinterJob
file.encoding = UTF-8
java.specification.version = 1.8
user.name = root
java.class.path = /usr/local/jdk/lib/:/usr/local/jdk/jre/lib/
java.vm.specification.version = 1.8
sun.arch.data.model = 64
sun.java.command = HelloWorld
java.home = /usr/local/jdk1.8.0_241/jre
user.language = en
java.specification.vendor = Oracle Corporation
awt.toolkit = sun.awt.X11.XToolkit
java.vm.info = mixed mode
java.version = 1.8.0_241
java.ext.dirs = /usr/local/jdk1.8.0_241/jre/lib/ext:/usr/java/packages/lib/ext
sun.boot.class.path = /usr/local/jdk1.8.0_241/jre/lib/resources.jar:/usr/local/jdk1.8.0_241/jre/lib/rt.jar:/usr/local/jdk1.8.0_241/jre/lib/sunrsasign.jar:/usr/local/jdk1.8.0_241/jre/lib/jsse.jar:/usr/local/jdk1.8.0_241/jre/lib/jce.jar:/usr/local/jdk1.8.0_241/jre/lib/charsets.jar:/usr/local/jdk1.8.0_241/jre/lib/jfr.jar:/usr/local/jdk1.8.0_241/jre/classes
java.vendor = Oracle Corporation
file.separator = /
java.vendor.url.bug = http://bugreport.sun.com/bugreport/
sun.io.unicode.encoding = UnicodeLittle
sun.cpu.endian = little
sun.cpu.isalist =
VM Flags:
Non-default VM flags: -XX:CICompilerCount=2 -XX:InitialHeapSize=268435456 -XX:MaxHeapSize=536870912 -XX:MaxNewSize=178913280 -XX:MinHeapDeltaBytes=196608 -XX:NewSize=89456640 -XX:OldSize=178978816 -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseFastUnorderedTimeStamps
Command line: -Xms256m -Xmx512m
[root@tomcat ~]#jinfo -flags 21407
Attaching to process ID 21407, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.241-b07
Non-default VM flags: -XX:CICompilerCount=2 -XX:InitialHeapSize=268435456 -XX:MaxHeapSize=536870912 -XX:MaxNewSize=178913280 -XX:MinHeapDeltaBytes=196608 -XX:NewSize=89456640 -XX:OldSize=178978816 -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseFastUnorderedTimeStamps
Command line: -Xms256m -Xmx512m
jstat：输出指定的java进程的统计信息
jstat -help|-options
jstat -<option> [-t] [-h<lines>] <vmid> [<interval> [<count>]]
[<interval> [<count>]]
interval：时间间隔，单位是毫秒；
count：显示的次数；
返回可用统计项列表
# jstat -options
-class：class loader
-compiler：JIT
-gc：gc
-gccapacity：统计堆中各代的容量
-gccause：
-gcmetacapacity
-gcnew：新生代
-gcnewcapacity
-gcold：老年代
-gcoldcapacity
-gcutil
-printcompilation
[root@tomcat ~]#jstat -gc 21407
S0C S1C S0U S1U EC EU OC OU MC MU CCSC CCSU YGC YGCT FGC FGCT GCT
8704.0 8704.0 1563.6 0.0 69952.0 58033.0 174784.0 0.0 9344.0 8830.0 1152.0 1013.0 2 0.050 0 0.000 0.050
YGC：新生代的垃圾回收次数；
YGCT：新生代垃圾回收消耗的时长；
FGC：Full GC的次数；
FGCT：Full GC消耗的时长；
GCT：GC消耗的总时长；
3次，一秒一次
[root@tomcat ~]#jstat -gcnew 21407 1000 3
S0C S1C S0U S1U TT MTT DSS EC EU YGC YGCT
8704.0 8704.0 1563.6 0.0 15 15 4352.0 69952.0 62794.3 2 0.050
8704.0 8704.0 1563.6 0.0 15 15 4352.0 69952.0 62794.3 2 0.050
8704.0 8704.0 1563.6 0.0 15 15 4352.0 69952.0 63074.5 2 0.050
程序员常用堆栈情况查看工具
jstack：查看指定的java进程的线程栈的相关信息；
jstack [-l] <pid>
jstack -F [-m] [-l] <pid>
-l：long listings，会显示额外的锁信息，因此，发生死锁时常用此选项；
-m：混合模式，既输出java堆栈信息，也输出C/C++堆栈信息；
-F：当使用“jstack -l PID"无响应，可以使用-F强制输出信息；
先获得一个java进程ID，然后jinfo
[root@tomcat ~]#jstack -l 21407
2020-02-15 13:49:56
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.241-b07 mixed mode):
"RMI TCP Connection(4)-10.0.0.101" #16 daemon prio=9 os_prio=0 tid=0x00007f279c29e800 nid=0x5753 runnable [0x00007f279b181000]
java.lang.Thread.State: RUNNABLE
at java.net.SocketInputStream.socketRead0(Native Method)
......
jmap：Memory Map, 用于查看堆内存的使用状态；
查看进程堆内存情况
[root@tomcat ~]#jmap -heap 21407
Attaching to process ID 21407, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.241-b07
using thread-local object allocation.
Mark Sweep Compact GC
Heap Configuration:
MinHeapFreeRatio = 40
MaxHeapFreeRatio = 70
MaxHeapSize = 536870912 (512.0MB)
NewSize = 89456640 (85.3125MB)
MaxNewSize = 178913280 (170.625MB)
OldSize = 178978816 (170.6875MB)
NewRatio = 2
SurvivorRatio = 8
MetaspaceSize = 21807104 (20.796875MB)
CompressedClassSpaceSize = 1073741824 (1024.0MB)
MaxMetaspaceSize = 17592186044415 MB
G1HeapRegionSize = 0 (0.0MB)
Heap Usage:
New Generation (Eden + 1 Survivor Space):
capacity = 80543744 (76.8125MB)
used = 4893096 (4.666419982910156MB)
free = 75650648 (72.14608001708984MB)
6.075078903707283% used
Eden Space:
capacity = 71630848 (68.3125MB)
used = 3301800 (3.1488418579101562MB)
free = 68329048 (65.16365814208984MB)
4.609466580655306% used
From Space:
capacity = 8912896 (8.5MB)
used = 1591296 (1.517578125MB)
free = 7321600 (6.982421875MB)
17.85386029411765% used
To Space:
capacity = 8912896 (8.5MB)
used = 0 (0.0MB)
free = 8912896 (8.5MB)
0.0% used
tenured generation:
capacity = 178978816 (170.6875MB)
used = 0 (0.0MB)
free = 178978816 (170.6875MB)
0.0% used
4926 interned Strings occupying 389832 bytes.
jhat：Java Heap Analysis Tool
jmap [option] <pid>
查看堆空间的详细信息：
jmap -heap <pid>
查看堆内存中的对象的数目：
jmap -histo[:live] <pid>
live：只统计活动对象；
保存堆内存数据至文件中，而后使用jvisualvm或jhat进行查看：
jmap -dump:<dump-options> <pid>
dump-options:
live dump only live objects; if not specified, all objects in the heap are dumped.
format=b binary format
file=<file> dump heap to <file>
