Not able to turn off G1 GC in JDK-9 preview builds?

[Thomas Schatzl]

Hi,

On Thu, 2016-03-31 at 11:44 +0300, Attila-Mihaly Balazs wrote:
> Hello,
> 
> I'm trying to do some benchmarks and was curious what effect using / 
> not using G1 GC had on it. However I'm unable to turn it off in the
> latest JDK-9 beta build (111):

Only trying to disable collectors and not giving an alternative will
fall back to the default collector since you need a collector to run.
Since G1 is the default collector in this build, it will fall back to
G1.

The same happens if you only specify -XX:-ParallelGC on the JDK8
command line.

> ~/jdk-9-111/bin/java -XX:-UseG1GC -XX:+PrintFlagsFinal -version |
> grep
> UseG1GC
>      bool UseG1GC                                  :=
> true                                {product}
> java version "9-ea"
> Java(TM) SE Runtime Environment (build 9-ea+111)
> Java HotSpot(TM) 64-Bit Server VM (build 9-ea+111, mixed mode)
> 
> With JDK-8 this works as expected:

In JDK8 the default collector is parallel gc.

> Any pointers as to what my be the issue? I understand that there is a
> push to use G1 GC by default in Java 9, however it was my 
> understanding that the previous GC algorithms will still be
> available.

Explicitly enable a different collector, e.g. -XX:+UseParallelGC.

You do not need to specify -XX:-Use<default>GC if you want to enable a
different collector.

Thanks,
  Thomas