Thank you very much for your input gentlemen. Increasing PermGen is a great 
idea, because I do see my server giving me out of memory permgen error at 
least twice a day and now it makes sense why, I was thinking my -Xmx 
settings 1024m should take care of my needs for now and that was wrong, I 
set MaxPermSize=256m and the server seem to be fine for now, keeping my 
fingers crossed. 
 Now regarding shared/lib directory I thought that every application loads 
its own copy of those libraries, but if its only one time load and since all 
my applications are identical copies (only data changes) I might as well 
move all my classes into shared, before I only had struts, hibernate jars 
and so on.... That wouldnt create any thread safety issues would it? Thanks 
again for your time, this helps a lot!

 On 8/17/05, Peter Crowther <[EMAIL PROTECTED]> wrote: 
> > From: Oleg [mailto:[EMAIL PROTECTED]
> > I am trying to approximate the amount of memory my server
> > will need running
> > tomcat. I understand that a lot depends on how the appication handles
> > resources, however at this point I am trying to figure out
> > what will be the
> > mimimum needed. In my case I have virtual hosting setup, with
> > all hosts
> > sharing the same libraries, so I have struts, hibernate,...
> > all sitting in
> > shared/lib directory of Tomcat. Would I be correct to
> > estimate that Tomcat
> > will atleast need
> >
> > n(number of users/applications) * mb(total size of shared/lib)
> As Chuck has already pointed out, no (but I'm going to try a slightly
> different angle on it :-) ). Each class that is loaded from shared/lib
> will be loaded by the Shared classloader, so you'll only have one copy
> of the class in your JVM. Jars are compressed, so the sizes of the
> loaded classes will be larger than the bytes occupied on disk; but not
> all of the classes from a jar will be loaded, so the sizes will probably
> be smaller. Note, however, that any classes in the webapp's WEB-INF/lib
> *will* be loaded once per webapp. If you have large numbers of
> applications, you may want to put more common libraries in shared/lib,
> and you may also wish to increase the size of the permanent generation
> (PermGen) in the JVM's memory model as this is where the classes are
> stored.
> Your per-session and per-page data will dwarf the space required for
> classes; and, as Chuck pointed out, the only way to find out these sizes
> is to profile the app. This will also make sure that you're not going
> to fall foul of any other performance limits, such as CPU use or disk
> bandwidth.
> - Peter
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