Java - 3 adet long[] array'da 100M+ veri merge işlemi

package exam1;

import java.time.Duration;
import java.time.Instant;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Random;

/**
 *
 * @author Furkan
 */

//VM OPTIONS -> -Xincgc -Xmx4g -Xms4g

public final class Exam1 {

private static final int LENGTH = 100000000;

private volatile long[] m_testArr1 = null;
private volatile long[] m_testArr2 = null;
private volatile long[] m_testArr3 = null;

private volatile long[] m_merged = null;

private Random m_r = new Random(System.currentTimeMillis());


public static void main(String[] args) {
    Exam1 exam = new Exam1();

    Instant start1 = Instant.now();
    System.out.println("Fill Started");
    exam.Fill();

    Instant end1 = Instant.now();
    System.out.println("Fill Ended : " + Duration.between(start1, end1)); 

    Instant start2 = Instant.now();
    System.out.println("Merge Started");
    exam.Merge();
    Instant end2 = Instant.now();
    System.out.println("Merge Ended : " + Duration.between(start1, end1)); 

    Instant start3 = Instant.now();
    System.out.println("DupRemove Started");
    exam.DupRemove();
    Instant end3 = Instant.now();
    System.out.println("DupRemove Ended : " + Duration.between(start1, end1)); 
}

private void Fill(){
    this.m_testArr1 = new long[Exam1.LENGTH];
    this.m_testArr2 = new long[Exam1.LENGTH];
    this.m_testArr3 = new long[Exam1.LENGTH];

    for (int i = 0; i < Exam1.LENGTH; i++) {
        this.m_testArr1[i] = this.m_r.nextLong();
        this.m_testArr2[i] = this.m_r.nextLong();
        this.m_testArr3[i] = this.m_r.nextLong();
    }
}

private void Merge(){
    this.m_merged = this.TryMerge(this.m_testArr1, this.m_testArr2, this.m_testArr3);
}

 private void DupRemove(){
    this.m_merged = this.RemoveDuplicates(this.m_merged);
}

public long[] TryMerge(long[] arr1, long[] arr2, long[] arr3){
    int aLen = arr1.length;
    int bLen = arr2.length;
    int cLen = arr3.length;

    int len = aLen + bLen + cLen;

    //TODO: Use BitSize for RAM optimize. IDK how to use...

    //OutOfMemory Exception on this line. 
    long[] mergedArr = new long[len];
    this.m_merged = new long[len];

    //long[] mergedArr = (long[]) Array.newInstance(long.class, aLen+bLen+cLen);

    System.arraycopy(arr1, 0, mergedArr, 0, aLen);
    System.arraycopy(arr2, 0, mergedArr, aLen, bLen);
    System.arraycopy(arr3, 0, mergedArr, (aLen + bLen), cLen);


    return mergedArr;
}

//!!!NOT WORKING!!!
private long[] RemoveDuplicates(long[] arr){
    HashSet<Long> set = new HashSet<Long>();

    final int len = arr.length;
    for(int i = 0; i < len; i++){
        set.add(arr[i]);
    }

    long[] clean = new long[set.size()];
    int i = 0;
    for (Iterator<Long> it = set.iterator(); it.hasNext();) {
        clean[i++] = it.next();
    }
    return clean;
}
}