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From Christopher Schultz <ch...@christopherschultz.net>
Subject Re: Tomcat Memory and Garbage Collection questions...
Date Sat, 07 Nov 2009 01:40:27 GMT
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Trevin,

On 11/5/2009 5:26 PM, Johnson, Trevin (Contractor) wrote:
> I see odd behavior. Our tomcat setting is set for a max memory
> setting of 256Mb in our Development Environment. Yet it goes over
> 256Mb. Up to 290Mb. I assumed that it would never go over 256Mb in
> task manager. Is that correct?

Is the "odd behavior" you describe the failure of your process to stay
below 256MiB of memory allocation? See Chuck's response for why your
process can (and will) take up more than just the heap.

I also seem to recall that, even as the heap expands and contracts (say,
between some arbitrarily small size and somewhere just shy of 256MiB),
the JVM will never release memory back to the operating system for use
by other programs. I'm not sure if this is just on Microsoft Windows or
also on other systems, but I have observed it myself and it's nothing to
worry about -- assuming your Java processes are sufficiently
high-priority that allowing them to retain this system is acceptable.

If you're just seeing your JVM take more than the max heap space you
expected, then you need to change your expectations. If nothing else
seems amiss, I'd say your server is probably running rather well.

- -chris
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