java：线上问题排查常用手段

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CountDownLatch;

/**
 * Created by 菩提树下的杨过 on 05/09/2017.
 */
public class OOMTest {

    public static void main(String[] args) throws InterruptedException {
        CountDownLatch latch = new CountDownLatch(1);
        int max = 10000;
        List<Person> list = new ArrayList<>(max);
        for (int j = 0; j < max; j++) {
            Person p = new Person();
            p.setAge(100);
            p.setName("菩提树下的杨过");
            list.add(p);
        }
        System.out.println("ready!");
        latch.await();
    }


    public static class Person {
        private String name;
        private int age;

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public int getAge() {
            return age;
        }

        public void setAge(int age) {
            this.age = age;
        }
    }
}　　

using thread-local object allocation.
Parallel GC with 4 thread(s)  //当前使用的GC方式(并行GC)

Heap Configuration:  //堆内存配置
   MinHeapFreeRatio         = 0   //对应jvm启动参数-XX:MinHeapFreeRatio设置JVM堆最小空闲比率(java8默认0)
   MaxHeapFreeRatio         = 100 //对应jvm启动参数-XX:MaxHeapFreeRatio设置JVM堆最大空闲比率 
   MaxHeapSize              = 8388608 (8.0MB) //对应jvm启动参数-XX:MaxHeapSize=设置JVM堆的最大大小(或-Xmx参数)
   NewSize                  = 5242880 (5.0MB) //对应jvm启动参数-XX:NewSize=设置JVM堆的‘新生代’的默认
   MaxNewSize               = 5242880 (5.0MB) //对应jvm启动参数-XX:MaxNewSize=设置JVM堆的‘新生代’的最大大小 
   OldSize                  = 3145728 (3.0MB) //对应jvm启动参数-XX:OldSize=设置JVM堆的‘老生代’的大小 
   NewRatio                 = 2 //对应jvm启动参数-XX:NewRatio=:‘新生代’和‘老生代’的大小比率 
   SurvivorRatio            = 8 //对应jvm启动参数-XX:SurvivorRatio=设置年轻代中Eden区与Survivor区的大小比值 
   MetaspaceSize            = 21807104 (20.796875MB)
   CompressedClassSpaceSize = 1073741824 (1024.0MB)
   MaxMetaspaceSize         = 17592186044415 MB
   G1HeapRegionSize         = 0 (0.0MB)

Heap Usage: //堆内存使用情况 
PS Young Generation
Eden Space: //Eden区分布
   capacity = 2621440 (2.5MB) //Eden区总容量
   used     = 2328088 (2.2202377319335938MB) //Eden区已使用
   free     = 293352 (0.27976226806640625MB) //Eden区剩余容量
   88.80950927734375% used
From Space: //其中一个Survivor区的内存分布
   capacity = 1572864 (1.5MB)
   used     = 360448 (0.34375MB)
   free     = 1212416 (1.15625MB)
   22.916666666666668% used
To Space: //另一个Survivor区的内存分布
   capacity = 1048576 (1.0MB)
   used     = 0 (0.0MB)
   free     = 1048576 (1.0MB)
   0.0% used
PS Old Generation //当前的Old区内存分布 
   capacity = 3145728 (3.0MB)
   used     = 1458968 (1.3913803100585938MB)
   free     = 1686760 (1.6086196899414062MB)
   46.37934366861979% used

3759 interned Strings occupying 298824 bytes.

import java.util.concurrent.CountDownLatch;

/**
 * Created by 菩提树下的杨过 on 05/09/2017.
 */
public class OOMTest {

    public static void main(String[] args) throws InterruptedException {
        CountDownLatch latch = new CountDownLatch(1);
        int max = 100;
        for (int i = 0; i < max; i++) {
            Thread t = new Thread() {
                public void run() {
                    try {
                        Thread.sleep(50);
                    } catch (InterruptedException e) {
                        Thread.currentThread().interrupt();
                    }
                }
            };
            t.setName("thread-" + i);
            t.start();
        }
        Thread t = new Thread() {
            public void run() {
                int i = 0;
                while (true) {
                    i = (i++) / 10;
                }
            }
        };
        t.setName("BUSY THREAD");
        t.start();
        System.out.println("ready");
        latch.await();
    }

}

import java.util.ArrayList;
import java.util.List;

/**
 * Created by 菩提树下的杨过 on 05/09/2017.
 */
public class OOMTest {

    public static void main(String[] args) throws InterruptedException {
        List<String> list = new ArrayList<>();
        while (true) {
            Thread.sleep(10);
            list.add("菩提树下的杨过" + System.currentTimeMillis());
        }
    }
}