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moniotring JVM heap size

I have a java application that creates a fairfew jvm's on the server it runs on.

What is the best way to measure the utaliseation of each JVM is.

I want to be able to see which JVMs are about to run out of memory in its heap.

are there any trick bits of softwar eout their that that might cater for my need that anyone knows of! ;)

Willa
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willa666
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willa666
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Ajay-SinghCommented:
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Ajay-SinghCommented:
> are there any trick bits of softwar eout their that that might cater
> for my need that anyone knows of! ;)


Quite simple theory: create an object, when you are done with it make sure that its dereferenced.
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willa666Author Commented:
Hello Ajay-Singh

will this let me moniotr multiple(20-50) Jvms at once?

I am only concerned with knowing if a JVM is going to run out of memory.
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Ajay-SinghCommented:
I think you should - but more than monitoring this tool points out memory leaks and cpu, gc timings.


To monitor only monitoring, you can start the jvm process with jmx enabled and monitor on jmx console. With this you can monitor heap/cpu usage very easily.

More: http://java.sun.com/javase/technologies/core/mntr-mgmt/javamanagement/
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girionisCommented:
You might also try JProbe SUite (http://www.quest.com/jprobe/) (not free though).
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maclemaCommented:
Here is a little chunk of HTML/JSP I use to monitor my JVM's.
<%!
    String displaySize(long size) {
            long ONE_KB = 1024;
               long ONE_MB = ONE_KB * ONE_KB;
               long ONE_GB = ONE_KB * ONE_MB;
      
        String displaySize;

        if (size / ONE_GB > 0) {
            displaySize = String.valueOf(size / ONE_GB) + " GB";
        } else if (size / ONE_MB > 0) {
            displaySize = String.valueOf(size / ONE_MB) + " MB";
        } else if (size / ONE_KB > 0) {
            displaySize = String.valueOf(size / ONE_KB) + " KB";
        } else {
            displaySize = String.valueOf(size) + " bytes";
        }
        return displaySize;
    }
%>

<div><b>Max. Heap Size:</b> <%= displaySize(Runtime.getRuntime().maxMemory()) %></div>
<div><b>Cur. Heap Size:</b> <%= displaySize(Runtime.getRuntime().totalMemory()+Runtime.getRuntime().freeMemory()) %></div>
<div><b>Used Memory:</b> <%= displaySize(Runtime.getRuntime().totalMemory()) %></div>
<div><b>Free Memory:</b> <%= displaySize(Runtime.getRuntime().freeMemory()) %></div>

Hope that helps

Matt
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maclemaCommented:
Also keep this in mind:

Max Heap is the maximum allowable size that the heap can grow to.

Curr Hear is the currently allocated space that can be used for the heap.

Used Memory is the amount of the current heap that is used.

Free Memory is the amount of space left in the currently allocated heap size.

You will receive an out of memory error once the heap tries to expand past the maximum heap size.

- Matt
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willa666Author Commented:
Hi maclema:

Is there a list of all the monitoring servlets anywhere on the net?

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maclemaCommented:
What do you mean by a list of monitoring servlets?
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