JVM uses tools to analyze classic cases of OOM

1 Heap overflow

1.1 JVM Parameters

 -XX:+PrintGCDetails -XX:MetaspaceSize=64m -XX:+HeapDumpOnOutOfMemoryError  -XX:HeapDumpPath=heap/heapdump.hprof -XX:+PrintGCDateStamps -Xloggc:logs/gc-oomHeap.log -Xms30M  -Xmx30M

1.2 CODE

/** * @Description: -XX:+PrintGCDetails -XX:MetaspaceSize=64m -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=heap/heapdump.hprof -XX:+PrintGCDateStamps -Xloggc:logs/gc-oomHeap.log -Xms30M -Xmx30M * * * PrintGCDetails:  Print GC details  * MetaspaceSize:  Meta space size is 64m * HeapDumpOnOutOfMemoryError、HeapDumpPath： Generate dump file  * -XX:+PrintGCDateStamps -Xloggc:logs/gc-oomHeap.log: GC Plus time 、GC Generate logs  * -Xms30M -Xmx30M：  Heap space size  * * * * @Author: rosh * @Date: 2022/6/22 22:10 */
public class HeapOomTest {
    


    public static void main(String[] args) {
    
        List<People> list = new ArrayList<>();
        while (true) {
    
            list.add(new People());
        }
    }

}

1.3 result

1.4 analysis GC journal

# Visit website , choice GC journal 
https://gceasy.io/

1.5 VisualVM analysis dump file

1.6 Solutions

  1、 Check for large object assignments , The most likely is large array allocation  
​  2、 adopt jmap command , Put the heap memory dump Come down , Use MAT Wait for tools to analyze , Check for memory leaks 
​  3、 If no memory leak is found , Use  -Xmx  Increase heap memory 

2 Meta space overflow

2.1 Parameters

-XX:+PrintGCDetails  -XX:+PrintGCDateStamps -Xloggc:log/gc-oomMeta.log -XX:MetaspaceSize=40m -XX:MaxMetaspaceSize=40m  -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=heap/heapdumpMeta.hprof  -Xms60M  -Xmx60M

2.2 CODE

/** * @Description: -XX:+PrintGCDetails -XX:+PrintGCDateStamps -Xloggc:log/gc-oomMeta.log -XX:MetaspaceSize=40m -XX:MaxMetaspaceSize=40m -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=heap/heapdumpMeta.hprof -Xms60M -Xmx60M * * GC Log correlation ：-XX:+PrintGCDetails -XX:+PrintGCDateStamps -Xloggc:logs/gc-oomMeta.log *  Meta space size setting ：-XX:MetaspaceSize=40m -XX:MaxMetaspaceSize=40m *  Pile up dump file :-XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=heap/heapdumpMeta.hprof * -Xms60M -Xmx60M:  Heap size settings  * * @Author: rosh * @Date: 2022/6/22 22:57 */
public class MetaspaceOomTest {
    

        public static void main(String[] args) {
    

        while (true) {
    
            Enhancer enhancer = new Enhancer();
            enhancer.setSuperclass(People.class);
            enhancer.setUseCache(false);
            enhancer.setCallback((MethodInterceptor) (o, method, params, methodProxy) -> {
    
                System.out.println(" I've enhanced ,JAVA  Can save the Chinese people ");
                return methodProxy.invokeSuper(o, params);
            });

            People people = (People) enhancer.create();
            people.sayHello();
        }

    }

}

2.3 result

2.4 VisualVM see

2.5 see dump

2.6 Solution

1.  Check whether the permanent generation space or meta space is set too small 
2.  Check if there are a lot of reflection operations in the code 
3. dump After through mat Check if there are a large number of proxy classes generated by reflection