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From "Shapira, Yoav" <>
Subject RE: heap size config
Date Tue, 17 Jun 2003 18:36:50 GMT

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 []
>Sent: Tuesday, June 17, 2003 1:16 PM
>To: Tomcat Users List;
>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" <>
>To: "Tomcat Users List" <>; "Billy Ng"
>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
>> phase.  The effects are negligible during that phase and none
>> >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
>> -Xms equal to -Xmx is useful only if you're going to have a constant
>> memory usage more or less throughout the life of your JVM.  If you
>> and stay low until peak demand comes in, keeping -Xms low is more
>> GC and other operations are always faster on a smaller heap.
>> Of course, nothing is more beneficial then having stress tests to run
>> 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
>> __________________________________
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