jinfo——实时查看和修改 JVM 配置参数

女爷i 2022-09-07 04:00 324阅读 0赞

# 一 点睛 #

jinfo(Configuration Info for Java)：查看虚拟机配置参数信息，也可用于调整虚拟机的配置参数。

在很多情况卡，Java 应用程序不会指定所有的 Java 虚拟机参数。而此时，开发人员可能不知道某一个具体的 Java 虚拟机参数的默认值。在这种情况下，可能需要通过查找文档获取某个参数的默认值。这个查找过程可能是非常艰难的。但有了 jinfo 工具，开发人员可以很方便地找到 Java 虚拟机参数的当前值。

基本使用语法为：jinfo \[options\] pid

说明：java 进程 ID 必须要加上

<table> 
 <tbody> 
 <tr> 
 <td> 选项 </td> 
 <td> 选项说明 </td> 
 </tr> 
 <tr> 
 <td> no option </td> 
 <td> 输出全部的参数和系统属性 </td> 
 </tr> 
 <tr> 
 <td> -flag name </td> 
 <td> 输出对应名称的参数 </td> 
 </tr> 
 <tr> 
 <td> -flag [+-]name </td> 
 <td> 开启或者关闭对应名称的参数 只有被标记为 manageable 的参数才可以被动态修改 </td> 
 </tr> 
 <tr> 
 <td> -flag name=value </td> 
 <td> 设定对应名称的参数 </td> 
 </tr> 
 <tr> 
 <td> -flags </td> 
 <td> 输出全部的参数 </td> 
 </tr> 
 <tr> 
 <td> -sysprops </td> 
 <td> 输出系统属性 </td> 
 </tr> 
 </tbody> 
</table>

官方帮助文档：

https://docs.oracle.com/en/java/javase/11/tools/jinfo.html

# 二 实战 #

## 1 代码 ##

package chaper02;
    
    import java.util.Scanner;
    
    public class ScannerTest {
        public static void main(String[] args) {
            Scanner scanner = new Scanner(System.in);
            String info = scanner.next();
        }
    }

## 2 jinfo -sysprops PID——可以查得由System.getProperties()取得的参数 ##

> F:\\svn\\19\_byzb\_back\\branches\\JVMDemo3>jinfo -sysprops 1552
> 
> Attaching to process ID 1552, please wait...
> 
> Debugger attached successfully.
> 
> Server compiler detected.
> 
> sun.desktop = windows
> 
> sun.cpu.isalist = amd64

## 3 jinfo -flags PID——查看曾经赋过值的一些参数 ##

> F:\\svn\\19\_byzb\_back\\branches\\JVMDemo3>jinfo -flags 3528
> 
> Attaching to process ID 3528, please wait...
> 
> Debugger attached successfully.
> 
> Server compiler detected.
> 
> JVM version is 25.251-b08
> 
> Non-default VM flags: -XX:CICompilerCount=4 -XX:InitialHeapSize=62914560 -XX:MaxHeapSize=62914560 -XX:MaxNewSize=20971520 -XX:MinHeapDeltaBytes=524288 -XX:NewSize=20971520 -XX:OldSize=41943040 -XX:SurvivorRatio=8 -XX:+UseCompressedC
> 
> lassPointers -XX:+UseCompressedOops -XX:+UseFastUnorderedTimeStamps -XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGC
> 
> Command line:  -Xms60m -Xmx60m -XX:SurvivorRatio=8 -javaagent:D:\\ProgramFiles\\JetBrains\\IDEA\\lib\\idea\_rt.jar=53644:D:\\ProgramFiles\\JetBrains\\IDEA\\bin -Dfile.encoding=UTF-8

## 4 jinfo -flag name PID——查看某个 java 进程的具体参数的值 ##

> F:\\svn\\19\_byzb\_back\\branches\\JVMDemo3>jinfo -flag UseParallelGC 5208
> 
> \-XX:+UseParallelGC
> 
> F:\\svn\\19\_byzb\_back\\branches\\JVMDemo3>jinfo -flag UseSerialGC 5208
> 
> \-XX:-UseSerialGC
> 
> F:\\svn\\19\_byzb\_back\\branches\\JVMDemo3>jinfo -flag MaxHeapSize 5208
> 
> \-XX:MaxHeapSize=104857600

## 5 查看被标记为 manageable 的参数 ##

> F:\\svn\\19\_byzb\_back\\branches\\JVMDemo3>java -XX:+PrintFlagsFinal -version|find "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\}
> 
> java version "1.8.0\_251"
> 
> Java(TM) SE Runtime Environment (build 1.8.0\_251-b08)
> 
> Java HotSpot(TM) 64-Bit Server VM (build 25.251-b08, mixed mode)

## 6 jinfo -flag \[+-\]name——开启或关闭对应名称的参数 ##

> F:\\svn\\19\_byzb\_back\\branches\\JVMDemo3>jinfo -flag PrintGCDetails 5209
> 
> \-XX:-PrintGCDetails
> 
> F:\\svn\\19\_byzb\_back\\branches\\JVMDemo3>jinfo -flag +PrintGCDetails 5209
> 
> F:\\svn\\19\_byzb\_back\\branches\\JVMDemo3>jinfo -flag PrintGCDetails 5209
> 
> \-XX:+PrintGCDetails

## 7 jinfo -flag name = value —— 设置对应名称的参数 ##

> F:\\svn\\19\_byzb\_back\\branches\\JVMDemo3>jinfo -flag MaxHeapFreeRatio 5209
> 
> \-XX:MaxHeapFreeRatio=100
> 
> F:\\svn\\19\_byzb\_back\\branches\\JVMDemo3>jinfo -flag MaxHeapFreeRatio=90 5209
> 
> F:\\svn\\19\_byzb\_back\\branches\\JVMDemo3>jinfo -flag MaxHeapFreeRatio 5209
> 
> \-XX:MaxHeapFreeRatio=90

# 三 拓展 #

## 1 java -XX:+PrintFlagsInitial 查看所有 JVM 参数启动的初始值 ##

> \[Global flags\]
> 
> intx ActiveProcessorCount = -1 \{product\}
> 
> uintx AdaptiveSizeDecrementScaleFactor = 4 \{product\}
> 
> uintx AdaptiveSizeMajorGCDecayTimeScale = 10 \{product\}
> 
> uintx AdaptiveSizePausePolicy = 0 \{product\}
> 
> ...

## 2 java -XX:+PrintFlagsFinal 查看所有 JVM 参数的最终值 ##

> \[Global flags\]
> 
> intx ActiveProcessorCount = -1 \{product\}
> 
> ...
> 
> intx CICompilerCount := 4 \{product\}
> 
> uintx InitialHeapSize := 333447168 \{product\}
> 
> uintx MaxHeapSize := 1029701632 \{product\}
> 
> uintx MaxNewSize := 1774714880 \{product\}

## 3 java -XX:+PrintCommandLineFlags 查看哪些已经被用户或者 JVM 设置过的详细的 XX 参数的名称和值 ##

> \-XX:InitialHeapSize=332790016 -XX:MaxHeapSize=5324640256 -XX:+PrintCommandLineFlags -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGC