Why does Java , running in -server mode, say that the version is “mixed-mode”?

Question

Why does Java , running in -server mode, say that the version is "mixed-mode" ? When I see that, does it mean that the JVM didn't truly load in pure server mode?

Answer 1

server mode does not mean "not mixed". Those are different settings.

Mixed does mean that the JVM will mix compiled and interpreted code. You could optionally switch to fully interpreted mode with the switch -Xint (usually you don't want to do this).

Server mode means that the hot-spot-compiler will run with server-settings. The general assumption is that VMs in server-mode are long-running, so optimizations will be done with this in mind.

So if you see mixed mode, that is no sign that your VM is not running in server-mode.

EDIT: If you want to check what is really running, try the output of

System.out.println(System.getProperty("java.vm.name"));
System.out.println(System.getProperty("java.vm.info"));

At least for the Sun VM or OpenJDK this will give you a hint. You might notice that you'll always run the Server VM if you are on a 64 bit system.

Answer 2

Hotspot Virtual Machine

Both the client and server Hotspot compilers are included in the Java Runtime Environment.

By default the client compiler is enabled, but for intense server-side applications, you can run the server compiler with the -server runtime option. The Hotspot virtual machine normally runs in a mixed mode, as seen in the -version output. Mixed mode means Hotspot dynamically compiles Java bytecodes into native code when a number of criteria have been met, including the number of times the method has been run through the interpreter. Mixed runtime mode normally results in the best performance.