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

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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>
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