Increasing Heap Size upto 6GB

Question

I was looking at the following article: Increase heap size in Java

Now I have a program that needs about 5GB memory and while doing what was told in the article (that is increasing heap size by using -Xmx5g in the arguments field), I am still getting

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space

My system is Windows 7 (64 bit) with 8GB RAM. Am I doing something wrong? If yes, how shall I proceed to get 5GB of heap memory or it is just not feasible for my system to handle?

Note: I have to do calculations with a 2D matrix that is of 25K*25K size having all non-zero values. Hence I cannot use sparse matrix as well.

can you please list the parameter as you have configured them ? — Salah, Mar 27 '14 at 08:24
Set 6G of memory and see result. I think, 5G is not enough to your program or you have not 5G free system memory. — DmitryKanunnikoff, Mar 27 '14 at 08:25
@salah-I just added -Xmx5g in the arguments field if that what you were asking. — Shrikant Kakani, Mar 27 '14 at 08:26
@DmitryTsechoev: tried that as well.. still got the same exception. — Shrikant Kakani, Mar 27 '14 at 08:26
1. Do you use java 64bit? 2. Check memory usage with some appropriate tool (eg. *jvisualvm*) — agad, Mar 27 '14 at 08:27
What is the element type in the matrix? Reducing `double` to `float` (if your able to give up precision) will halve the memory consumption. — Bathsheba, Mar 27 '14 at 08:27
As an alternative, you can persist semi-calculated value on disc temporarily. Read-write at certain row and column — Erdinç Taşkın, Mar 27 '14 at 08:31
@Beginner Then you should put the -Xmx5G in the VM arguments instead of program arguments :) — locoyou, Mar 27 '14 at 08:33
@locoyou: oh man !! so that was the problem.. lets see.. I think I might get away with your solution :) — Shrikant Kakani, Mar 27 '14 at 08:43

AlexR · Answer 1 · 2014-03-27T08:34:41.713

OutOfMemoryError is thrown when JVM does not have enough memory for objects being allocated. If you defined heap of 5G this almost definitely mean that you have a kind of memory leak. For example I can write very simple code that will cause OutOfMemoryError at any environment:

List<String> list = new LinkedList<>();
while(true) {
    list.add("a");
}

Run this code and wait several seconds. OutOfMemoryError will be thrown. This is because I add strings to list and never clean it.

I believe that something similar happens with your application.

I understand, that it is not so trivial as my example, so you will probably have to use profiler to debug it and understand the reason of your memory leak.

EDIT: I've just saw that you are working with 25K*25K martrix. It means that you have 625M cells. You have not mentioned the type of the matrix but if it is int that occupies 4 bytes you need 625*4=2500M=2.5G memory, so 5G should be enough.

Please try to analyze what else happens in your program and where your memory is spent.

score 1 · Answer 2 · answered Mar 27 '14 at 08:36

1

5G/(25K*25K) ~ 8 bytes.

Generously assuming that you program does not use memory except for that matrix, each matrix element must take no more than 8 bytes.

You should calculate at least approximate memory requirements to check whether it is even possible to handle problem of such size on your hardware. For example, if you need a 2D array of MxN size of double values then you need at least 8*M*N bytes of memory.

answered Mar 27 '14 at 08:36

Oleg Estekhin

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Well (8*M*N)b + 128m I'd say, you need breathing space for the application outside of that matrix too ;) – Gimby Mar 27 '14 at 09:47

Increasing Heap Size upto 6GB

2 Answers2