Set Xms/Xmx based on Jconsole memory monitoring

I used jconsole to monitor memory usage of a java server program running with JDK 1.5.0.3 in Linux, in order to set the Xms/Xmx option for the program. I found that memory usage of the process is no more than 4MB. But somehow after setting the Xms/Xmx to be 4MB, the server program could not run (its client programs could not connect to it). So I tuned the Xms/Xmx value and when I raised them to 512MB, then the server worked again.
I don't understand why this happens. Is Jconsole reading not a good reflection of the heap memory usage? Or something else might be wrong?
Thanks for any idea on this.

<Jos van der Velden> wrote in message news:[email protected]..
Hi,
We are using weblogic 8.1 sp3 with the jdk1.4.2_05 (we do not use jrocket) for the implementation of some of our solutions.
We are trying to optimize performance generally on servers with 2 processors and 4-8Gb of RAM, and some exceptions such as forinstance a test-machine we have at the moment with 4 processors and 20 Gb of RAM.
>
Although we seem to be able to improve performance by raising the settings for Xms and Xmx to 1024m ( even though our developmenttests done in the labs in Cary, NC - USA have resulted in recommendations that show lower values ) we would like to have some more
info because not all info we have points to the same directions. For instance
1. What are theoretically the maximum values for these settings (in particular Xms and Xmx)?Theoretically the maximum is a memory space addressable by a process.
2. Should Xms and Xmx be set to the same value (as mentioned in info from your website - see below), or are there situations wheredifferent values could improve performance ?
For a production environment Xms and Xmx should be equal so that JVM doesn't
spend time shrinking and expanding heap.
3. Is there other general advice you can give for improving performance using these settings ?Generally it is a good idea to keep heap under 1G. Bigger heap means longer GC-s.
You may consider co-locating cluster nodes running in separate JVMs if you have
enough CPUs and extensive RAM. Generally 2 CPUs per weblogic instance is enough.
Regards,
Slava Imeshev

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Text from the above link
==================
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Set Xms/Xmx based on Jconsole memory monitoring

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