jvm-hotspot

Are OpenJDK VM and Oracle Hotspot VM still two different JVMs? I can't seem to find any somewhat official documentation on anything about OpenJDK VM. Even in OpenJDK homepage there is an HotSpot Group which develops HotSpot VM. The HotSpot group is comprised of developers involved in the design, implementation, and maintanence of the HotSpot virtual machine However if I check java -version on my Windows machine it prints out Java HotSpot(TM) 64-Bit Server VM But on my Ubuntu VPS OpenJDK 64-Bit Server VM If those are two different VMs what are the main differences between them? Do they have

I know Microsoft .NET uses the CLR as a JIT compiler while Java has the Hotspot. What Are the differences between them? They are very different beasts. As people pointed out, the CLR compiles to machine code before it executes a piece of MSIL. This allows it in addition to the typical dead-code elimination and inlining off privates optimizations to take advantage of the particular CPU architecture of the target machine (though I'm not sure whether it does it). This also incurs a hit for each class (though the compiler is fairly fast and many platform libraries are just a thin layer over the

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 default value for XX:MaxDirectMemorySize? John Gardner From http://www.docjar.com/html/api/sun/misc/VM.java.html i see: 163 // A user-settable upper limit on the maximum amount of allocatable direct 164 // buffer memory. This value may be changed during VM initialization if 165 // "java" is launched with "-XX:MaxDirectMemorySize=<size>". 166 // 167 // The initial value of this field is arbitrary; during JRE initialization 168 // it will be reset to the value specified on the command line, if any, 169 // otherwise to Runtime.getRuntime.maxDirectMemory(). 170 // 171 private static

I have a Java app which shows different GC behaviors in different environments. In one environment, the heap usage graph is a slow sawtooth with major GCs every 10 hours or so, only when the heap is >90% full. In another environment, the JVM does major GCs every hour on the dot (the heap is normally between 10% and 30% at these times). My question is, what are the factors which cause the JVM to decide to do a major GC? Obviously it collects when the heap is nearly full, but there is some other cause at play which I am guessing is related to an hourly scheduled task within my app (although