JVM信息查看

摘要：系列垃圾回收基础的编译策略的三大基础算法的三大高级算法策略的评价指标信息查看通用日志解读的数据结构类初始化顺序对象结构及大小计算的类加载机制对象分配简要流程年老代过大有什么影响空间溢出实例关于线程与序本文主要讲述如何查看应用的信息。

jvm系列

垃圾回收基础

JVM的编译策略

GC的三大基础算法

GC的三大高级算法

GC策略的评价指标

JVM信息查看

GC通用日志解读

jvm的card table数据结构

Java类初始化顺序

Java对象结构及大小计算

Java的类加载机制

Java对象分配简要流程

年老代过大有什么影响

Survivor空间溢出实例

关于Object=null

Java线程与Xss

本文主要讲述如何查看java应用的jvm信息。

Java -XX:+PrintCommandLineFlags 这个参数的作用是显示出VM初始化完毕后所有跟最初的默认值不同的参数及它们的值。 （JDK5以上支持）

-XX:+PrintFlagsFinal显示所有可设置的参数及它们的值（ JDK 6 update 21开始才可以用），默认是不包括diagnostic或experimental系的。要在-XX:+PrintFlagsFinal的输出里看到这两种参数的信息，分别需要显式指定-XX:+UnlockDiagnosticVMOptions / -XX:+UnlockExperimentalVMOptions

-XX:+PrintFlagsInitial看下所有XX参数的默认值，也可以通过-XX:+PrintFlagsFinal进行对比出修改过的参数，当然通过-XX:+PrintCommandLineFlags就可以自动显示出修改过的值

jinfo -flags pid

[xixicat@cloud01 ~]$ jps 
9275 Jps
22855 start.jar
22869 XmlConfiguration
20967 Application
[xixicat@cloud01 ~]$ jinfo -flags 22869
Attaching to process ID 22869, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 23.21-b01
-javaagent:/opt/xixicat/apps/lib/jolokia-jvm-1.1.0-agent.jar=port=23061 -Xloggc:/var/xixicat/logs/app.gc.log.201504301631 -XX:ErrorFile=/var/xixicat/logs/app.vmerr.log.201504301631 -XX:HeapDumpPath=/var/xixicat/logs/app.heaperr.log.201504301631 -Xmx5g -Xms5g -XX:MaxPermSize=256m -XX:+HeapDumpOnOutOfMemoryError -XX:+DisableExplicitGC -XX:+PrintGCDetails -XX:+PrintGCDateStamps -XX:+PrintGCTimeStamps -XX:+PrintGCApplicationStoppedTime -XX:+PrintHeapAtGC -XX:+PrintTenuringDistribution -XX:+PrintCommandLineFlags -XX:+PrintAdaptiveSizePolicy -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:MaxGCPauseMillis=100 -XX:StringTableSize=49999 -Djetty.home=/opt/xixicat/apps/server/jetty-distribution-8.1.9.v20130131 -Dapp.port=8061 -Dmedis_environment=online -Dcore.step=app -DSTOP.PORT=38061 -Djetty.port=8061 -Dcom.sun.management.jmxremote.authenticate=false -Dapp.logdir=/var/xixicat/logs -DLog4jContextSelector=org.apache.logging.log4j.core.async.AsyncLoggerContextSelector -Dapp.ip=10.64.28.207 -Dapp.context -Dcom.sun.management.jmxremote.ssl=false -Djetty.context -Djava.io.tmpdir=/tmp -Djetty.host=cloud01 -Djava.net.preferIPv6Addresses=false -DSTOP.KEY=stop_app -Dcore.zookeeper=127.0.0.1:9331 -Djetty.logs=/var/xixicat/logs -Dapp.workdir=/opt/xixicat/apps/app/work -Dapp.key=app -Dfile.encoding=UTF-8 -Dapp.host=cloud01 -Duser.timezone=GMT+08 -Djetty.appkey=app -DAsyncLogger.WaitStrategy=Block -Dcom.sun.management.jmxremote.port=8199 -Djetty.home=/opt/xixicat/apps/server/jetty-distribution-8.1.9.v20130131 -Denvironment=online

java -XX:+PrintFlagsFinal -version |grep manageable
通过选项-XX:+PrintFlagsFinal可以列出所有的JVM flag，而其中的标注为manageable 的flag则是值得我们关注的部分。这些flag可通过JDK management interface（-XX:+PrintFlagsFinal）动态修改。

-XX:+PrintGCDetails

jinfo -flag -PrintGCDetails 12278

[xixicat@cloud01 ~]$ jmap -heap 22869
Attaching to process ID 22869, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 23.21-b01
using thread-local object allocation.
Garbage-First (G1) GC with 4 thread(s)
Heap Configuration:
   MinHeapFreeRatio = 40
   MaxHeapFreeRatio = 70
   MaxHeapSize      = 5368709120 (5120.0MB)
   NewSize          = 1363144 (1.2999954223632812MB)
   MaxNewSize       = 17592186044415 MB
   OldSize          = 5452592 (5.1999969482421875MB)
   NewRatio         = 2
   SurvivorRatio    = 8
   PermSize         = 20971520 (20.0MB)
   MaxPermSize      = 268435456 (256.0MB)
   G1HeapRegionSize = 2097152 (2.0MB)
Heap Usage:
G1 Heap:
   regions  = 2560
   capacity = 5368709120 (5120.0MB)
   used     = 3826721792 (3649.4462890625MB)
   free     = 1541987328 (1470.5537109375MB)
   71.27824783325195% used
G1 Young Generation:
Eden Space:
   regions  = 1068
   capacity = 2808086528 (2678.0MB)
   used     = 2239758336 (2136.0MB)
   free     = 568328192 (542.0MB)
   79.76101568334578% used
Survivor Space:
   regions  = 29
   capacity = 60817408 (58.0MB)
   used     = 60817408 (58.0MB)
   free     = 0 (0.0MB)
   100.0% used
G1 Old Generation:
   regions  = 1000
   capacity = 2499805184 (2384.0MB)
   used     = 1524048896 (1453.4462890625MB)
   free     = 975756288 (930.5537109375MB)
   60.96670675597735% used
Perm Generation:
   capacity = 171966464 (164.0MB)
   used     = 170752872 (162.8426284790039MB)
   free     = 1213592 (1.1573715209960938MB)
   99.29428565792921% used
48213 interned Strings occupying 5246936 bytes.

查看对象分布

[xixicat@cloud01 ~]$ jcmd 15308 VM.flags
15308:
-XX:+DisableExplicitGC -XX:ErrorFile=/var/xixicat/logs/app.vmerr.log.201505071655 -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/var/xixicat/logs/app.heaperr.log.201505071655 -XX:InitialHeapSize=5368709120 -XX:+ManagementServer -XX:MaxGCPauseMillis=100 -XX:MaxHeapSize=5368709120 -XX:MaxPermSize=268435456 -XX:+PrintAdaptiveSizePolicy -XX:+PrintCommandLineFlags -XX:+PrintGC -XX:+PrintGCApplicationStoppedTime -XX:+PrintGCDateStamps -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintHeapAtGC -XX:+PrintTenuringDistribution -XX:StringTableSize=49999 -XX:+UnlockExperimentalVMOptions -XX:+UseCompressedOops -XX:+UseG1GC