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From Peter Lin <tcw00l...@yahoo.com>
Subject RE: Memory Settings On Tomcat
Date Thu, 10 Jun 2004 02:14:38 GMT

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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> > > 
> > > 
> > >
> >
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