CODEWITHSUNDEEP
java
anthomedal
anthomedal

Reputation: 21

java.lang.OutOfMemoryError: Java heap space error not solved by -Xmx and -Xms

I'm beginner in java and I tried to make a code which sums two matrixes, but I have the error :

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
    at Main.main(Main.java:11)

I tried all this commands : 

$ java Main
$ java Main -Xmx2048m
$ java Main -Xms1024m
$ java Main -Xms1024m -Xmx2048m
$ java -Xmx2048m Main
$ java -Xms1024m Main
$ java -Xms1024m -Xmx2048m Main

But all give the same error message...

This is the code : 

public class Main
{
    public static void main(String[] args)
    {
        final int n = 10000;

        double A[][] = new double[n][n];
        double B[][] = new double[n][n];
        double S[][] = new double[n][n];

        int i,j;

        for (i = 0; i<n; i++)
        {
            for (j = 0; j<n; j++)
            {
                A[i][j] = 1.0d / ((double) i*j);
                B[i][j] = 1.0d / ((double) i*j);
            }
        }

        for (i = 0; i<n; i++)
        {
            for (j = 0; j<n; j++)
            {
                S[i][j] = A[i][j] + B[i][j];
            }
        }
    }
}

So as you can see, this code need ~ 3x8x10000 B = 240 000 B < 2048 MB. My java's version : 

$ java -version
openjdk version "11.0.4" 2019-07-16
OpenJDK Runtime Environment (build 11.0.4+11-post-Ubuntu-1ubuntu218.04.3)
OpenJDK 64-Bit Server VM (build 11.0.4+11-post-Ubuntu-1ubuntu218.04.3,     mixed mode, sharing)

Upvotes: 1

Views: 451

Answers (2)

Sujay Mohan
Sujay Mohan

Reputation: 952

I am able to run your code without any Xms or Xmx setting. My Laptop is having 16 GB Ram.

enter image description here

Upvotes: 0

Simon Kocurek
Simon Kocurek

Reputation: 2166

The flags work, but your math does not check out.

You have 3 arrays, each with 10 000 * 10 000 * 8B values.
For that you need 3 * 10 000 * 10 000 * 8 Bytes... which is 2289 MB.
That is already more than 2048.

To add to that, each of those 3 arrays contains 10 000 references... but the memory overhead of that is minuscule (less than 1MB) compared to the values.

Upvotes: 1

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