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From "Caldarale, Charles R" <>
Subject RE: tomcat memory usage
Date Fri, 29 Jan 2010 15:10:52 GMT
> From: Hüsnü Þentürk []
> Subject: Re: tomcat memory usage
> Is following classifications true for memory usage of Java ?

Pretty much, but you're missing ancillary bits such as libraries, OS-created structures, statically
linked code, dynamically generated code, stacks, and probably other things I'm leaving out.
 Running a process in a modern OS is complicated.

> Sum of PermGen and Heap memory usage smalller then 600,980 KB which
> I see on Task Manager. Can you explain the reason of this difference?

Just because the virtual space is reserved doesn't mean it's actually being used in real memory.
 I don't know which of the memory values you chose to display in Task Manager, but it's probably
real memory usage, which is only that part of the process space that the OS happens to have
loaded at that instant.  Nearly all components of memory usage change over time, both in virtual
space and real, and there is no definitive relationship between the two.  In other words,
the Task Manager number is not terribly useful for tuning a Java execution, but it does provide
some information when you're looking at the system as a whole.

 - Chuck

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