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moniotring JVM heap size

Posted on 2006-11-30
Last Modified: 2012-06-27
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! ;)

Question by:willa666
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Expert Comment

ID: 18051321
LVL 23

Expert Comment

ID: 18051327
> 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.

Author Comment

ID: 18051453
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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Expert Comment

ID: 18051657
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/
LVL 35

Expert Comment

ID: 18052343
You might also try JProbe SUite (http://www.quest.com/jprobe/) (not free though).

Expert Comment

ID: 18320970
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


Accepted Solution

maclema earned 500 total points
ID: 18320987
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

Author Comment

ID: 18323696
Hi maclema:

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


Expert Comment

ID: 18335058
What do you mean by a list of monitoring servlets?

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