Hi Yoav,
Just the person I was hoping to hear from! Thanks for
responding.
> It's not a good idea to set -Xmx to a higher amount
> than the amount of
> physical RAM: the JVM will thrash once it reaches
> much less than 512MB.
Oh, my, so -Xmx512m is the best I can do.
> Your understanding is good and correct on the above
> issues.
Thank you for confirming that.
> And there's the ever-present (which is why it's
> often forgotten) advice:
> you might want to get more physical RAM. It's
> pretty cheap, and 512MB
> isn't that much for a server nowadays.
Quite correct, but I don't make that decision. That's
left to our enlightened corporate IT staff. ;)
I'll look into those other JVM settings. Thanks again
for your usual sage advice. Sincerely, %
--- "Shapira, Yoav" <[EMAIL PROTECTED]> wrote:
>
> Hi,
>
> >I've got Tomcat 4.1.29 installed to run as a
> service
> >under JDK 1.4.1_05 on this Windows 2000 server. The
> >Tomcat memory settings on startup are -Xms64m and
> >-Xmx1024m. The server has 512MB of physical RAM
>
> It's not a good idea to set -Xmx to a higher amount
> than the amount of
> physical RAM: the JVM will thrash once it reaches
> much less than 512MB.
>
> >My understanding is that Java's garbage collection
> >will reclaim heap-allocated memory to the JVM, but
> not
> >necessarily to the OS. Is this true? What this
> means
> >is that a Windoze server admin could look at the
> task
> >manager and see a large memory usage for Tomcat,
> but
> >that doesn't necessarily reflect Tomcat's current
> >usage.
> >
> >It's more like a high water mark on a pier: it'll
> show
> >the highest value that Tomcat has used, but the
> real
> >value will be lower if the garbage collector runs
> and
> >the tide goes out. If you read a lot of objects
> into
> >session you could end up with a big high water
> mark.
>
> Your understanding is good and correct on the above
> issues.
>
> >(1) Is my understanding of the interaction between
> the
> >JVM and OS memory management correct?
> >(2) Are there any other tuning settings for Tomcat
> >that I need to look at?
>
> Yes to 1, and likely yes to 2. Check out the
> different garbage
> collector implementations, and the directives for
> setting old and young
> generation sizes. Your case is a classic one for
> setting a small old
> generation size relative to the young generation
> size: maybe even a 10-1
> or slightly less ratio of young size to old size.
>
> And there's the ever-present (which is why it's
> often forgotten) advice:
> you might want to get more physical RAM. It's
> pretty cheap, and 512MB
> isn't that much for a server nowadays.
>
> Yoav
>
>
>
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