Diagnose RSS leak in Java when heap is stable

Question

I am using a simple test program that I run for a few hours.

public static void main(String[] args)  {
    for (int i=1; i<500; i++) {
        run();
    }
}

public static void run() {
    new Thread(new Runnable() {

        @Override
        public void run() {
            while (true) {
                new String("Hello World");
            }
        }
    }).start();
}

When I monitor the process either through PS or pmap, the RSS portion increases while jvisualvm reports heap is stable.

If I sum up all the RSS anon mappings, they are increasing over time.

I am using Centos 5.7 x64 with Sun JDK 1.6.0_31.

Should the RSS be increasing over time?

Does your program creates 499 threads that run an infinite loop ? — Yann Droneaud, Feb 21 '12 at 13:28
hi, im not sure what RSS means but try changing this new String("Hello World"); to this "Hello World"; if you dont make it create a new string each time you might not have a memory leak. what is the point of this exercise anyway ? — yael alfasi, Feb 21 '12 at 13:33
@yael: RSS stands for resident set size, you can read more at http://en.wikipedia.org/wiki/Resident_set_size — , Feb 21 '12 at 16:49

score 0 · Answer 1 · answered Feb 21 '12 at 16:49

0

RSS can increase over time as background tasks bring more code/resources into memory. In your example it shouldn't be much. Note: if you use a shared library in another JVM instance that shared library is loaded into memory and this could increase your RSS.

It usually best to find the simplest example which demonstrates your problem. Does it have to be 500 threads, or just the number of cores you have? Does it happen when you have one busy thread? What if you create a new Object() instead? What if you busy wait without creating an object?

answered Feb 21 '12 at 16:49

Peter Lawrey

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Definitely have less cores than 500 threads. I am trying to understand the behavior of why the RSS is increasing in this simplistic example when this is the only JAVA app running. I am incline to think that it is due to a shared library loading into memory? – Nora Olsen Feb 22 '12 at 02:34
Its hard to tell unless you simplify your example. It could be a problem caused by excessive context switching or GCing. It could be specific to your machine in some way. It could be cause by connecting monitoring tools, or using your shared library in other processes. – Peter Lawrey Feb 22 '12 at 07:57

Diagnose RSS leak in Java when heap is stable

1 Answers1