JVM调优

junziln2022年1月12日约 3558 字大约 12 分钟

JVM调优

启动一个springboot服务

jmap -histo

jmap -histo 62536 #查看历史生成的实例

jmap -histo:live 62536 #查看当前存活的实例，执行过程中可能会触发一次full gc

jmap -heap 62536

jmap -dump:format=b,file=eureka.hprof 14660

public class OOMTest {

   public static List<Object> list = new ArrayList<>();

   // JVM设置    
   // -Xms10M -Xmx10M -XX:+PrintGCDetails -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=D:\jvm.dump 
   public static void main(String[] args) {
      List<Object> list = new ArrayList<>();
      int i = 0;
      int j = 0;
      while (true) {
         list.add(new User(i++, UUID.randomUUID().toString()));
         new User(j--, UUID.randomUUID().toString());
      }
   }
}

可以用 jvisualvm 命令工具导入该dump文件分析

用jstack加进程id查找死锁，见如下示例

public class DeadLockTest {

   private static Object lock1 = new Object();
   private static Object lock2 = new Object();

   public static void main(String[] args) {
      new Thread(() -> {
         synchronized (lock1) {
            try {
               System.out.println("thread1 begin");
               Thread.sleep(5000);
            } catch (InterruptedException e) {
            }
            synchronized (lock2) {
               System.out.println("thread1 end");
            }
         }
      }).start();

      new Thread(() -> {
         synchronized (lock2) {
            try {
               System.out.println("thread2 begin");
               Thread.sleep(5000);
            } catch (InterruptedException e) {
            }
            synchronized (lock1) {
               System.out.println("thread2 end");
            }
         }
      }).start();

      System.out.println("main thread end");
   }
}

jvisualvm自动检测死锁

package com.junziln.study.maintest.jvm;

/**
 * 运行此代码，cpu会飙高
 */
public class Cpu {

    public static final int initData = 666;
    public static User user = new User();

    public int compute() {  //一个方法对应一块栈帧内存区域
        int a = 1;
        int b = 2;
        int c = (a + b) * 10;
        return c;
    }

    public static void main(String[] args) {
        Math math = new Math();
        while (true){
            math.compute();
        }
    }
}

丢到对应目录下在linux执行 java com.junziln.study.maintest.jvm.Cpu

使用命令top -p ，显示你的java进程的内存情况，pid是你的java进程号，比如19663
按H，获取每个线程的内存情况
找到内存和cpu占用最高的线程tid，比如19664
转为十六进制得到 0x4cd0，此为线程id的十六进制表示
执行 jstack 19663|grep -A 10 4cd0，得到线程堆栈信息中 4cd0 这个线程所在行的后面10行，从堆栈中可以发现导致cpu飙高的调用方法
查看对应的堆栈信息找出可能存在问题的代码.

Jinfo pid

查看正在运行的Java应用程序的扩展参数

查看jvm的参数

jinfo -flags 62536

查看java系统参数

jstat -gccapacity pid

系统频繁Full GC导致系统卡顿

大家可以结合****推理下我们这个程序可能存在的一些问题

经过分析感觉可能会由于对象动态年龄判断机制导致full gc较为频繁

Arthas详解

https://alibaba.github.io/arthas/

Arthas

arthas-packaging-4.0.1-bin.zip

arthas 常用命令详解（dashboard、thread、jad、redefine等）_arthas dashboard-CSDN博客

# github下载arthas
wget https://alibaba.github.io/arthas/arthas-boot.jar
# 或者 Gitee 下载
wget https://arthas.gitee.io/arthas-boot.jar

package com.junziln.study.maintest.jvm;

import java.util.HashSet;

public class Arthas {

    private static HashSet hashSet = new HashSet();

    public static void main(String[] args) {
        // 模拟 CPU 过高
        cpuHigh();
        // 模拟线程死锁
        deadThread();
        // 不断的向 hashSet 集合增加数据
        addHashSetThread();
    }

    /**
     * 不断的向 hashSet 集合添加数据
     */
    public static void addHashSetThread() {
        // 初始化常量
        new Thread(() -> {
            int count = 0;
            while (true) {
                try {
                    hashSet.add("count" + count);
                    Thread.sleep(1000);
                    count++;
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }).start();
    }

    public static void cpuHigh() {
        new Thread(() -> {
            while (true) {

            }
        }).start();
    }

    /**
     * 死锁
     */
    private static void deadThread() {
        /** 创建资源 */
        Object resourceA = new Object();
        Object resourceB = new Object();
        // 创建线程
        Thread threadA = new Thread(() -> {
            synchronized (resourceA) {
                System.out.println(Thread.currentThread() + " get ResourceA");
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread() + "waiting get resourceB");
                synchronized (resourceB) {
                    System.out.println(Thread.currentThread() + " get resourceB");
                }
            }
        });

        Thread threadB = new Thread(() -> {
            synchronized (resourceB) {
                System.out.println(Thread.currentThread() + " get ResourceB");
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread() + "waiting get resourceA");
                synchronized (resourceA) {
                    System.out.println(Thread.currentThread() + " get resourceA");
                }
            }
        });
        threadA.start();
        threadB.start();
    }
}

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GC日志详解

%t 代表时间

-Xloggc:./gc-%t.log -XX:+PrintGCDetails -XX:+PrintGCDateStamps  -XX:+PrintGCTimeStamps -XX:+PrintGCCause  
-XX:+UseGCLogFileRotation -XX:NumberOfGCLogFiles=10 -XX:GCLogFileSize=100M

****

java -jar -Xloggc:./gc-adjust-%t.log -XX:MetaspaceSize=256M -XX:MaxMetaspaceSize=256M -XX:+PrintGCDetails -XX:+PrintGCDateStamps  
-XX:+PrintGCTimeStamps -XX:+PrintGCCause  -XX:+UseGCLogFileRotation -XX:NumberOfGCLogFiles=10 -XX:GCLogFileSize=100M 
microservice-eureka-server.jar

https://gceasy.io

JVM参数汇总查看命令

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贡献者

wangjialin

JVM调优

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