jvm虚拟机调优实战

使用命令 jps查看进程
使用jstat gc -1 5000查看内存占用和回收情况

正式测试是否跑job区别。大量的job,部分用户点击的热数据，不同时刻在跑 600-700对比 200 多了400-500m,代码原数据（不占用堆区）占了300m,所以堆空间=老年代（900）+700+7 约等于 1500-1600m。加上本地区（主要是栈内存（堆的对象引用指针） gc root+程序及计数器等小空间）

-server -XX:+PrintGCDetails -XX:+UseG1GC -XX:MaxGCPauseMillis=200 -Xms1600m -Xmx1600m -Xverify:none -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/log/plan01.hprof

full gc 过程： 15次=》old =>old大=》young变小=》young持续小=》young gc 频繁=>full gc

heap out of range: full gc =>old 不能变大（young 足够小）=》full gc后不能增大old的空间容不下新来的数据。

使用visal vm 和mat图形化分析

排查出问题：DruidDataSource比例最高在线程池的destroy线程中，排查可能是druid的数据源异常配置问题：

remove-abandoned: false=>remove-abandoned: true。

相关的其他配置正常

time-between-eviction-runs-millis: 60000 # 1 minute

min-evictable-idle-time-millis: 300000 # 5 minutes

useGlobalDataSourceStat: false

druid配置导致堆溢出（https://blog.csdn.net/lypeng13/article/details/121911981）

改动后观察启动后的 E O区的占用变化和之前趋势对比情况。和FullGc在相同时间的变化趋势

增大heap大小观察full gc
导出dump文件的方式 1. 命令 2. 工具 3. 代码

（1）docker file 文件启动文件，堆溢出自动导出

-XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/log/plan01.hprof

（2）

public class FullGCHeapDump {

private static HotSpotDiagnosticMXBean hotspotMBean;

private static long lastFullGCTime = -1; // To store the time of the last Full GC

private static final long THRESHOLD = 15000; // 2 seconds in milliseconds

// Method to trigger a heap dump
public static void dumpHeap(String filePath) {
    if (hotspotMBean == null) {
        try {
            hotspotMBean = ManagementFactory.newPlatformMXBeanProxy(
                    ManagementFactory.getPlatformMBeanServer(),
                    "com.sun.management:type=HotSpotDiagnostic",
                    HotSpotDiagnosticMXBean.class);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    try {
        // Dump the heap to the specified file
        hotspotMBean.dumpHeap(filePath, true);
        System.out.println("Heap dump created at: " + filePath);
    } catch (IOException e) {
        e.printStackTrace();
    }
}

@PostConstruct
public void postConstruct(){
    // Keep the application running so we can monitor GC events
    System.out.println("Monitoring for Full GC events...");
    // Register GC notification listener
    for (GarbageCollectorMXBean gcBean : ManagementFactory.getGarbageCollectorMXBeans()) {
        NotificationEmitter emitter = (NotificationEmitter) gcBean;
        emitter.addNotificationListener(new NotificationListener() {
            @Override
            public void handleNotification(Notification notification, Object handback) {
                String notificationType = notification.getType();
                if (notificationType.equals("com.sun.management.gc.notification")) {
                    com.sun.management.GarbageCollectionNotificationInfo info =
                            com.sun.management.GarbageCollectionNotificationInfo.from((javax.management.openmbean.CompositeData) notification.getUserData());

                    // Check if the GC type is "end of major GC" or "Full GC"
                    String gcAction = info.getGcAction();
                    System.out.println(gcAction);
                    if (gcAction.contains("end of major GC") || gcAction.contains("end of Full GC")) {
                        System.out.println("Full GC detected.");
                        long currentTime = System.currentTimeMillis();  // Get the current time

                        if (lastFullGCTime != -1 && (currentTime - lastFullGCTime) <= THRESHOLD) {
                            // If two Full GCs occurred within 2 seconds, trigger the heap dump
                            System.out.println("Two Full GCs detected within 2 seconds. Triggering heap dump...");
                            FullGCHeapDump.dumpHeap("heapdump.hprof");
                        }

                        // Update the time of the last Full GC
                        lastFullGCTime = currentTime;
                    }
                }
            }
        }, null, null);
    }
}

}

mat实例分析查找追踪堆栈和可能得内存泄漏点

模拟堆栈溢出

@PostMapping("post")

public void post(){

// simulate full gc

int maxValue = Integer.MAX_VALUE;

List list = new ArrayList<>();

while (true){

for (int i = 0; i < maxValue; i++) {

list.add(new AchResult());

}