metaspace

I wrote a program to simulate MetaSpace OOM. But I found that MetaSpace Size is almost always twice as big as Used MetaSpace . Why? I run my program with flag -XX:MaxMetaspaceSize=50m , the program throw OOM when Used MetaSpace reached about 25M rather than 50M, Why? expoter I think the following two experiment will explain what does the gap between MetaSpace Size and Used MetaSpace mean: EXP-1 : load one class per ClassLoader, I got this: EXP-2 : load five classes per ClassLoader, I got this: As Java 8 document says: Space is requested from the OS and then divided into chunks. A class loader

A java process that I'm running performs consistently well in the first hour or so that it runs. However, performance then rapidly degrades. When profiling I found that the metaspace garbage collection happened fairly frequently until the hour mark and then got out of control: I'm fairly sure I'll be able to fix this using the -XX:MaxMetaspaceSize option. However, I'd like to know more about why this behaviour might be occurring. I can't imagine why the garbage collection algorithm would behave like this. Does anyone have an explanation or advice about a better fix? Thanks the8472 You can try

I have this code to generate class dynamically and load it import javassist.CannotCompileException; import javassist.ClassPool; public class PermGenLeak { private static final String PACKAGE_NAME = "com.jigarjoshi.permgenleak."; public static void main(String[] args) throws CannotCompileException, InterruptedException { for (int i = 0; i < Integer.MAX_VALUE; i++) { ClassPool pool = ClassPool.getDefault(); pool.makeClass(PACKAGE_NAME + i).toClass(); Thread.sleep(3); } } } I launched this class against Java 7 (jdk1.7.0_60) and as expected it filled up PermGenSpace and heap remained unused image

What is the difference between Metaspace and Native memory ? Metaspace can be tracked using jconsole, jvisualvm, jstat cmds. It seems Native Memory can be tracked using jcmd. Link Is metaspace also Native Memory? Where do NIO buffers get stored? In the metaspace or native memory? sol4me Is metaspace also Native Memory? Yes, Metaspace is part of the Native Memory(process memory) and is limited by host operating system You can monitor it using jmap -permstat PID . If your application ends up allocating lot of memory in metaspace then it will effect the entire system not just the JVM.That's why

Are there any tools that are able to get Metaspace dump from a Java8 hotspot vm ? It seems you encounter a class loading leak. Use jmap -clstats PID to dump class loader statistics; jcmd PID GC.class_stats to print the detailed information about memory usage of each loaded class. The latter requires -XX:+UnlockDiagnosticVMOptions . The heap dump will also help, because each class in the Metaspace has a corresponding java.lang.Class instance in the heap. 来源： https://stackoverflow.com/questions/37919215/how-to-get-java8-metaspace-dump-not-heap-dump

I have read a lot about java memory areas, but looks like it is just a mess. Mostly due to the introduction of a new MetaSpace area instead of PermGen in java8. And there are questions now: What areas does the heap include in java8+ ? Where the static methods and variables are stored before java8 and java8+ ? Does the MetaSpace store anything except class meta-data info ? Does the structure of memory areas depend on the implementation of JVM ? Thank you for your answers. Does the structure of memory areas depend on the implementation of JVM ? Absolutely. PermGen or Metaspace are just