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From "Caldarale, Charles R" <Chuck.Caldar...@unisys.com>
Subject RE: memory required to run webapp without outofmemory
Date Mon, 03 Dec 2007 01:22:47 GMT
> From: teoh [mailto:second_comet@yahoo.com] 
> Subject: memory required to run webapp without outofmemory
> 
> is just by looking at tomcat manager, we can find out maximum memory
>  required to run webapp without out of memory?

Not really - it's much more complicated.  The JVM heap holds objects of
all types, including those from each webapp, ones used by Tomcat, ones
used by the JVM internally, etc.  The heap itself is partitioned into
various areas used for objects of different lifetimes, and garbage
collections occur when an area fills.  Looking at total heap usage at
any given instant of time won't really tell you what portion of the
usage depends on the number of requests that are being processed at that
instant.  Also, there's no guarantee that all requests will consume the
same amount of heap resources.

You generally want to configure the heap as large as you can without
provoking page swapping.  That will likely take some experimentation as
well monitoring.  JConsole provides a decent look at heap usage over
time, but you'll really nead a profiler if you want detailed information
about what your webapps are doing.

A link you may find interesting:
http://java.sun.com/javase/technologies/hotspot/gc/index.jsp

 - Chuck


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