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From "Caldarale, Charles R" <Chuck.Caldar...@unisys.com>
Subject RE: [OT] Jconsole Perform GC?
Date Tue, 09 Nov 2010 15:04:46 GMT
> From: Jeffrey Janner [mailto:Jeffrey.Janner@PolyDyne.com] 
> Subject: [OT] Jconsole Perform GC?

> Anyone know what exactly what kind of GC the "Perform GC" 
> button in Jconsole does?

The same one you get by calling System.gc() - a full GC.

> The initial work was mostly in the Eden space and Survivor 
> spaces for most of the day, then suddenly, a big chunk 
> (nearly 4GB) ended up in the Old Gen space and pretty much
> stayed there all night.

Anything too big for the Eden space will be allocated directly in tenured.

> Looking at the other individual graphs showed that there had 
> been several instances of GC performed by the JVM during that
> time, but it took my manual instance to clear the Old Gen.

Those were minor collections, cleaning out only the Eden space.

> Is this just "normal" JVM GC processing?

Yes, that's completely normal.  The JVM will not do a major (full) GC unless it has to - or
is forced by the API invocation.

 - Chuck


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