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From "Caldarale, Charles R" <Chuck.Caldar...@unisys.com>
Subject RE: Tomcat Memory and Garbage Collection questions...
Date Mon, 02 Nov 2009 21:06:16 GMT
> From: Johnson, Trevin (Contractor)
> [mailto:Trevin.Johnson@occ.treas.gov]
> Subject: Tomcat Memory and Garbage Collection questions...
> 
> When we restart the tomcat service our tomcat memory is about 120Mb. It
> keeps going up over the next few days util it reaches 700Mb and we have
> to reboot the server.

Why do you reboot?  Is the server unresponsive?

> 1.We do not see the memory going down for the tomcat service. Shouldn't
> the memory go down as well as up over this timespan

What are you using to show the memory usage?

> 2.Should the memory get to maximum 768Mb and then go back down or get
> recycled?

Depends on what you're looking at.  If it's Task Manager, it won't go down.  If you're using
JConsole to look at the heap, it should go up and down.

> 3.Is this a bug or what is normal behavior for the tomcat memory?

Depends; see above.

> 4.. How do we implement garbage collection for our windows server(-
> Xincgc)?

Garbage collection is always present.  Incremental GC can be useful to minimize pause times,
but it is more overhead and has some restrictions on just what it can collect.  Unless you
really think you need that option, I wouldn't set it right now.

I'd strongly recommend using JConsole to look at heap usage, then use a profiler if you find
that the heap usage does not stabilize.  You can also turn on -verbose:gc, and use jhat and
jmap to do basic heap analysis.

Some useful resources:
http://java.sun.com/j2se/1.5.0/docs/guide/vm/gc-ergonomics.html
http://java.sun.com/javase/technologies/hotspot/gc/index.jsp

 - Chuck


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