jvm 元空间

不念不忘少年蓝@ 2023-07-19 05:47 19阅读 0赞

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### jvm 元空间 ###

**java8 开始使用元空间（****元空间使用本地内存****）代替永久代实现方法区；**

**用来存储类信息、即时编译器编译后的热点代码等数据；**

**注意：java7开始在堆内存中存储常量池、静态变量**

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**相关参数**

**-XX:MetaspaceSize：**设置元空间的初始大小，**默认为20.8M**

**-XX:MaxMetaspaceSize：**设置元空间的最大值

**-XX:MinMetaspaceExpansion：**metaspace扩容的最小增量

**-XX:MaxMetaspaceExpansion：**metaspace扩容的最大增量

**-XX:MinMetaspaceFreeRatio：**剩余空间占比最小值，**默认40，**gc后剩余空间占比低于设定值值扩容

**-XX:MaxMetaspaceFreeRatio：**剩余空间占比最大值，**默认70，**gc后剩余空间占比高于设定值缩容

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**示例：元空间溢出测试**

public class Test {
    
        public static void main(String[] args){
            for (int i=0;i<10000;i++){
                Enhancer enhancer=new Enhancer();
                enhancer.setSuperclass(Test.class);
                enhancer.setUseCache(false);
                enhancer.setCallback((MethodInterceptor) (o, method, objects, methodProxy) -> methodProxy.invokeSuper(o,objects));
    
                System.out.println("metaspace test"+i);
                enhancer.create();
            }
        }
    }

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**虚拟机参数**

-XX:MaxMetaspaceSize=20m

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**控制台输出**

**部分输出**

metaspace test1620
    metaspace test1621
    metaspace test1622
    metaspace test1623
    metaspace test1624
    metaspace test1625
    metaspace test1626
    Exception in thread "main" org.springframework.cglib.core.CodeGenerationException: java.lang.OutOfMemoryError-->Metaspace
    	at org.springframework.cglib.core.ReflectUtils.defineClass(ReflectUtils.java:506)
    	at org.springframework.cglib.core.AbstractClassGenerator.generate(AbstractClassGenerator.java:363)
    	at org.springframework.cglib.proxy.Enhancer.generate(Enhancer.java:582)
    	at org.springframework.cglib.core.AbstractClassGenerator$ClassLoaderData.get(AbstractClassGenerator.java:131)
    	at org.springframework.cglib.core.AbstractClassGenerator.create(AbstractClassGenerator.java:319)
    	at org.springframework.cglib.proxy.Enhancer.createHelper(Enhancer.java:569)
    	at org.springframework.cglib.proxy.Enhancer.create(Enhancer.java:384)
    	at com.example.demo.test.Test.main(Test.java:19)
    Caused by: java.lang.OutOfMemoryError: Metaspace
    	at java.base/java.lang.ClassLoader.defineClass1(Native Method)
    	at java.base/java.lang.System$2.defineClass(System.java:2193)
    	at java.base/java.lang.invoke.MethodHandles$Lookup.defineClass(MethodHandles.java:975)
    	at java.base/jdk.internal.reflect.GeneratedMethodAccessor2.invoke(Unknown Source)
    	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    	at java.base/java.lang.reflect.Method.invoke(Method.java:567)
    	at org.springframework.cglib.core.ReflectUtils.defineClass(ReflectUtils.java:501)
    	... 7 more

**说明：****元空间内存不足，抛出OutOfMemoryError**