Peter Johnson [https://community.jboss.org/people/peterj] created the discussion

"Re: Not specifying an -Xms value"

To view the discussion, visit: https://community.jboss.org/message/743191#743191

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My recommendation is to not set -Xms the same as -Xmx on a development machine. 
Why? On such a machine you run numerous things, not just JBoss AS. In that 
event you want to use a little of your available memory as possible - most 
likely you won't be running the app server long enough for it to want to grab 
the rest of the memory for the heap.

On a production machine, always set -Xms to the same as -Xmx. Why? Because a 
production machine is tpyically a one-use machine (that is, other than the OS, 
only the app server will be running). And after runnign a while the app server 
will have grabbed all of the heap memory, and won't let it go. So you might as 
well give it all the heap memeory to start with. (There is also a small 
performance penalty for making the JVM continually ask the OS for more heap 
space, and also for causing the JVM to determine whether it needs nor space or 
can give space away. Setting -Xms and -Xmx to the same value avoids performing 
those calculations. But the performance difference on modern processors and RAM 
configurations is negligible.)
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