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From Michael Duffy <duff...@yahoo.com>
Subject RE: Memory Settings On Tomcat
Date Thu, 10 Jun 2004 13:07:18 GMT

Thank you, Peter, I'll give it a look.

%


--- Peter Lin <tcw00lfel@yahoo.com> wrote:
> 
> by the way, in case you haven't heard of it,
> 
> http://mc4j.sourceforge.net/
> 
> mc4J can monitor tomcat4 and generate nice graphs. I
> haven't used it, but it looks nice.
> 
> peter
> 
> 
> --- Michael Duffy <duffymo@yahoo.com> wrote:
> > 
> > Hi Peter,
> > 
> > Hiding in plain sight:
> > 
> >
>
http://jakarta.apache.org/tomcat/articles/performance.pdf
> > 
> > I apologize for overlooking it for all this time. 
> > I'll be sure to go through it right away.  Thanks
> -
> > %
> > 
> > 
> > --- Peter Lin <tcw00lfel@yahoo.com> wrote:
> > >  
> > > You might want to look at the VM performance
> > numbers
> > > in my Performance article. The link is listed on
> > the
> > > tomcat resources page.  Generally, tweaking the
> > > generations takes time.
> > >  
> > > for something, like XML, tweaking generation
> ratio
> > > doesn't help. 
> > >  
> > > peter
> > > 
> > > 
> > > Michael Duffy <duffymo@yahoo.com> wrote:
> > > 
> > > Hi Yoav,
> > > 
> > > > 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.
> > > 
> > > I've never checked this page out before, but at
> > your
> > > prompting I found it today:
> > > 
> > > http://java.sun.com/docs/hotspot/VMOptions.html
> > > 
> > > I believe the docs are telling me that the
> default
> > > value of XX:NewRatio=12 for Intel. Is that
> > correct? 
> > > If that's true, should I just leave the default?
> > > 
> > > I have no experience with setting any of these
> > > values.
> > > I've always used the JVM right out of the box
> (my
> > > ignorance).
> > > 
> > > What would be a minimum set of parameters to
> span
> > > this
> > > space? Thanks - %
> > > 
> > > 
> > > --- "Shapira, Yoav" 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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> > > > Thank you.
> > > > 
> > > > 
> > > >
> > >
> >
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