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From "Caldarale, Charles R" <Chuck.Caldar...@unisys.com>
Subject RE: OutOfMemoryError (but not really out of memory?) cause tomcatprocessesto hang
Date Thu, 08 Feb 2007 04:15:10 GMT
> From: Christopher Schultz [mailto:chris@christopherschultz.net] 
> Subject: Re: OutOfMemoryError (but not really out of memory?) 
> cause tomcatprocessesto hang
> 
> The collector itself requires the creation of Java objects on 
> the heap.

Not really.  The generational HotSpot collector does reserve a portion
of the heap into which it copies existing live objects (the To space of
the YoungGen area), but no real allocations occur there, nor are any new
objects created during the process.  Once the copy is done, another
portion of the YoungGen space is reserved for use by the next GC.

> Fair enough. But if Tomcat isn't happy, nobody's happy ;)

Depends on who you are; when you look at it from the guts of the JVM
(where I hang out), it ain't my problem :-)

> It's clear from the OP's heap stats that the Perm space is 
> busting. Odd, though: the MaxPermSpace is 64MB, but she is
> topping out at 20MB or so.

The boundary between the spaces is not readily movable, so the max often
can't be put to use once the heap is initialized.  As you know, running
out of PermGen is a pretty typical cause of OOMEs, especially with a
relatively small total heap such as this.  Need to set -XX:PermSize as
well as -XX:MaxPermSize to insure you really get the amount you want.

 - Chuck


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