Ken~

CMS (Concurrent Mark Sweep) is part of a multi-stage generational GC.  It is
the newest GC in a released version of the JVM (the G1 GC not having been
released yet).

With the below settings, the young gen is divided into Eden and two survivor
spaces.  The survivor spaces act as generations for young objects before
they are tenured into the old gen.  The concurrent mark sweep is only used
for the old generation and is far more than a simple mark-sweep GC.

If you are curious I can provide a somewhat more detailed explanation of the
different collectors and phases, but I can assure you that these settings
are very good defaults for high performance systems.

Matt

On Wed, Nov 17, 2010 at 10:37 PM, Ken Wesson <[email protected]> wrote:

> On Wed, Nov 17, 2010 at 10:12 PM, Matt Fowles <[email protected]>
> wrote:
> > Ken~
> > Not sure what jvm args you are running with, but not all GC settings will
> > sweep or clear the permgen.  You should try it with:
> > -XX:+CMSClassUnloadingEnabled
> > -XX:+CMSPermGenSweepingEnabled
> > -XX:+UseParNewGC
> > -XX:+UseConcMarkSweepGC
> > -XX:+CMSParallelRemarkEnabled
>
> Maybe I will.
>
> (Use a mark-sweep GC instead of the generational one that all newer
> JVMs use by default, though? That will really hurt GC performance.)
>
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