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From "Eric J. Pinnell" <e...@iCky.org>
Subject RE: heap size config
Date Tue, 17 Jun 2003 19:44:28 GMT
Forgive me for jumping in on this thread mid-way...

Keep in mind that 'top' is not the most accurate tool in the world.

As well as the way some unixs handle swap space.  Solaris, for example,
handles swap space like airlines sell tickets on planes.  They overbook
it.  So it might allocate the space but it won't ever use it.

Usually you don't want your java to swap at all.  It really slows you
down.

-e

On Tue, 17 Jun 2003, Shapira, Yoav wrote:

>
> Howdy,
> Please post the simplest unit test I can use to reproduce this,
> including the JMeter script that tracks swap space.  I'll be glad to see
> this one happen...
>
> What do you mean by "call a System Runtime" ?
>
> Yoav Shapira
> Millennium ChemInformatics
>
>
> >-----Original Message-----
> >From: Billy Ng [mailto:kwokng@earthlink.net]
> >Sent: Tuesday, June 17, 2003 1:16 PM
> >To: Tomcat Users List; yoavs@computer.org
> >Subject: Re: heap size config
> >
> >If you run top, and make a servlet to call a System Runtime.  Then, use
> >Jmeter to hammer it.  You will see the swap disk is create the same
> size as
> >the -Xms for each thread.  I have done the test with different sizes of
> >heap.  It is solid true.
> >
> >Billy Ng
> >
> >----- Original Message -----
> >From: "Yoav Shapira" <yoavs1@yahoo.com>
> >To: "Tomcat Users List" <tomcat-user@jakarta.apache.org>; "Billy Ng"
> ><evebill8@hotmail.com>
> >Sent: Tuesday, June 17, 2003 4:40 AM
> >Subject: Re: heap size config
> >
> >
> >> Howdy,
> >>
> >> >In Unix, java will make
> >> > 512MB swap every time we make a System Runtime call.
> >>
> >> I don't think so: can you prove the above?
> >>
> >> >Will this
> >> > hurt the Tomcat preformnace?
> >>
> >> Lowering -Xms will only slightly degrade performance during the
> >allocation
> >> phase.  The effects are negligible during that phase and none
> afterwards.
> >>
> >> >I read the article from Sun saying the -Xms and
> >> > -Xmx should be the same.  Is it always true?
> >>
> >> No.  Almost nothing in the realm of performance tuning is always
> true.
> >Setting
> >> -Xms equal to -Xmx is useful only if you're going to have a constant
> >level
> >> memory usage more or less throughout the life of your JVM.  If you
> start
> >low
> >> and stay low until peak demand comes in, keeping -Xms low is more
> >beneficial.
> >> GC and other operations are always faster on a smaller heap.
> >>
> >> Of course, nothing is more beneficial then having stress tests to run
> >against
> >> different combinations of settings.  That way you can see the actual
> >effect on
> >> your system intead of relying on me or someone else's article.
> >>
> >> Yoav Shapira
> >>
> >>
> >>
> >> =====
> >> Yoav Shapira
> >> yoavs@computer.org
> >>
> >> __________________________________
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