Java Performance笔记一

java监控工具

• jps 查看java进程号
• jcmd 打印java进程的基本类、线程、VM信息
• jhat 后加工工具，分析内存dump
• jmap 可以在线dump内存
• jinfo 查看jvm系统参数，可以动态设置参数
• jstat 可以查看gc和类加载情况
• jstack 查看线程堆栈情况
• jconsole 傻瓜式工具
• jvisualvm 傻瓜式工具，功能更强大，可以在线dump内存堆栈,也可以提供后处理工具

基本vm信息

下面命令中，其中的5090是进程号
VM启动时长

- jcmd process_id VM.uptime

JVM版本
- jcmd 5090 VM.version

JVM 命令行
- jcmd 5090 VM.command_line

系统属性
- jcmd 5090 VM.system_properties #输出结果等同于通过代码调用System.getProperties()
- 或者 jinfo -flags 5090
**注意:**jinfo要求jinfo版本和java进程的jvm版本要相同，否则会抛下面异常

/Users/lcz/remote_login>jinfo -sysprops 5090Attaching to process ID 5090, please wait...Exception in thread "main" java.lang.reflect.InvocationTargetException    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)    at java.lang.reflect.Method.invoke(Method.java:497)    at sun.tools.jinfo.JInfo.runTool(JInfo.java:108)    at sun.tools.jinfo.JInfo.main(JInfo.java:76)Caused by: java.lang.InternalError: void* type hasn't been seen when parsing int*    at sun.jvm.hotspot.HotSpotTypeDataBase.recursiveCreateBasicPointerType(HotSpotTypeDataBase.java:687)    at sun.jvm.hotspot.HotSpotTypeDataBase.lookupType(HotSpotTypeDataBase.java:131)    at sun.jvm.hotspot.HotSpotTypeDataBase.lookupOrCreateClass(HotSpotTypeDataBase.java:597)    at sun.jvm.hotspot.HotSpotTypeDataBase.createType(HotSpotTypeDataBase.java:717)    at sun.jvm.hotspot.HotSpotTypeDataBase.readVMTypes(HotSpotTypeDataBase.java:188)    at sun.jvm.hotspot.HotSpotTypeDataBase.<init>(HotSpotTypeDataBase.java:86)    at sun.jvm.hotspot.HotSpotAgent.setupVM(HotSpotAgent.java:403)    at sun.jvm.hotspot.HotSpotAgent.go(HotSpotAgent.java:305)    at sun.jvm.hotspot.HotSpotAgent.attach(HotSpotAgent.java:140)    at sun.jvm.hotspot.tools.Tool.start(Tool.java:185)    at sun.jvm.hotspot.tools.Tool.execute(Tool.java:118)    at sun.jvm.hotspot.tools.JInfo.main(JInfo.java:138)    ... 6 more

JVM 调优标志
The tuning flags in effect for an application can be obtained like this:
% jcmd process_id VM.flags [-all]

/Users/lcz/remote_login>jcmd 5090 VM.flags5090:-XX:InitialHeapSize=134217728 -XX:MaxHeapSize=2147483648 -XX:+UseCompressedOops -XX:+UseParallelGC /Users/lcz/remote_login>jcmd 5090 VM.flags -all5090:[Global flags]    uintx AdaptivePermSizeWeight                    = 20              {product}               uintx AdaptiveSizeDecrementScaleFactor          = 4               {product}               uintx AdaptiveSizeMajorGCDecayTimeScale         = 10              {product}               uintx AdaptiveSizePausePolicy                   = 0               {product}               uintx AdaptiveSizePolicyCollectionCostMargin    = 50              {product}      uintx InitialHeapSize                          := 134217728       {product}      .....   

如何使用调优标志

也可以通过下面命令，打印出平台默认值
java -XX:+PrintFlagsFinal -version
第一列表示类型，如bool intx uintx等
其中冒号表示这个标记是个非缺省值，如InitialHeapSize := 134217728
值改变的原因：
- 在命令行中直接设置
- 一些选项因为其它选项值被间接修改
- JVM计算的默认值ergonomically

最后一列表示不同的平台，例如：
- product means that the default setting of the flag is uniform across all platforms;
- pd productindicates that the default setting of the flag is platform-dependent.
- manageable (the flag’s value can be changeddynamicallyduringruntime)
- C2 diagnostic(theflagprovidesdiagnostic output for the compiler engineers to understand how the compiler is functioning)

是不是太多信息？

例如AllocatePrefetchLines 默认值是3，若要修改这个值需要考虑1.应用的prefetch性能；2.CPU运行程序的特性；3.对JVM本身性能的影响

只有manageable的标志可以修改

[root@localhost ~]# java -XX:+PrintFlagsFinal -version|grep manageable     intx CMSAbortablePrecleanWaitMillis            = 100                                 {manageable}     intx CMSTriggerInterval                        = -1                                  {manageable}     intx CMSWaitDuration                           = 2000                                {manageable}     bool HeapDumpAfterFullGC                       = false                               {manageable}     bool HeapDumpBeforeFullGC                      = false                               {manageable}     bool HeapDumpOnOutOfMemoryError                = false                               {manageable}    ccstr HeapDumpPath                              =                                     {manageable}    uintx MaxHeapFreeRatio                          = 100                                 {manageable}    uintx MinHeapFreeRatio                          = 0                                   {manageable}     bool PrintClassHistogram                       = false                               {manageable}     bool PrintClassHistogramAfterFullGC            = false                               {manageable}     bool PrintClassHistogramBeforeFullGC           = false                               {manageable}     bool PrintConcurrentLocks                      = false                               {manageable}     bool PrintGC                                   = false                               {manageable}     bool PrintGCDateStamps                         = false                               {manageable}     bool PrintGCDetails                            = false                               {manageable}     bool PrintGCID                                 = false                               {manageable}     bool PrintGCTimeStamps                         = false                               {manageable}

修改调优标志

jinfowhere <option> is one of:    -flag <name>         to print the value of the named VM flag    -flag [+|-]<name>    to enable or disable the named VM flag    -flag <name>=<value> to set the named VM flag to the given value    -flags               to print VM flags[root@localhost ~]# jps3145 Jps2538 WrapperSimpleApp[root@localhost ~]# jinfo -flag PrintGCDetails 2538-XX:-PrintGCDetails[root@localhost ~]# jinfo -flag +PrintGCDetails 2538[root@localhost ~]# jinfo -flag PrintGCDetails 2538-XX:+PrintGCDetails[root@localhost ~]# jinfo -flag -PrintGCDetails 2538[root@localhost ~]# jinfo -flag PrintGCDetails 2538-XX:-PrintGCDetails

线程信息
- jstack 进程号
另外可以参见第9章更详细信息

内存分析
- jstat -gcutil 16002 1s #观察内存变化情况
- jstat -gcutil ps -ef|grep Dhotdb.home|grep -v grep|awk '{print $2}' 1s #自动搜索pid然后跟踪内存
- jmap -dump:live,format=b,file=heap.bin 22741 #在线dump文件
- jhat heap.bin #观察内存变化情况
- 另外也可以通过Jconsole/JvisualVM直接dump，然后通过HPJmeter或者Eclipse的内存泄漏分析插件

类信息
jstat
下面2538是线程号

[root@localhost ~]# jstat -class 2538Loaded  Bytes  Unloaded  Bytes     Time     2312  4368.5        0     0.0       1.76[root@localhost ~]# jstat -printcompilation  2538 Compiled  Size  Type Method    1325     89    1 sun/reflect/GeneratedMethodAccessor5 invoke