I have following code, where I used HashMap (using two parallel arrays) for storing key-value pairs (key can have multiple values). Now, I have to store and load it for future use that's why I store and load it by using File Channel. Issue with this code is: I can store nearly 120 millions of key-value pairs in my 8 GB server (actually, I can allocate nearly 5 gb out of 8 gb for my JVM, and those two parallel arrays takes nearly 2.5 gb, other memory are used for various processing of my code). But, I have to store nearly 600/700 millions of key-value pairs. Can anybdoy help me how to modify this code thus I can store nearly 600/700 millions of key-value pairs. Or any comment on this will be nice for me. Another point, I have to load and store the hashmap to/from memory. It takes little bit long time using file channel. As per various suggestions of Stack Overflow, I didn't find faster one. I have used ObjectOutputStream, Zipped output stream also, however, slower than below code. Is there anyway to store those two parallel arrays in such a way thus loading time will be much faster. I have given below in my code a test case. Any comment on that will also be helpful to me.
import java.io.*;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.Arrays;
import java.util.Random;
import java.nio.*;
import java.nio.channels.FileChannel;
import java.io.RandomAccessFile;
public class Test {
public static void main(String args[]) {
try {
Random randomGenerator = new Random();
LongIntParallelHashMultimap lph = new LongIntParallelHashMultimap(220000000, "xx.dat", "yy.dat");
for (int i = 0; i < 110000000; i++) {
lph.put(i, randomGenerator.nextInt(200000000));
}
lph.save();
LongIntParallelHashMultimap lphN = new LongIntParallelHashMultimap(220000000, "xx.dat", "yy.dat");
lphN.load();
int tt[] = lphN.get(1);
System.out.println(tt[0]);
} catch (Exception e) {
e.printStackTrace();
}
}
}
class LongIntParallelHashMultimap {
private static final long NULL = -1L;
private final long[] keys;
private final int[] values;
private int size;
private int savenum = 0;
private String str1 = "";
private String str2 = "";
public LongIntParallelHashMultimap(int capacity, String st1, String st2) {
keys = new long[capacity];
values = new int[capacity];
Arrays.fill(keys, NULL);
savenum = capacity;
str1 = st1;
str2 = st2;
}
public void put(long key, int value) {
int index = indexFor(key);
while (keys[index] != NULL) {
index = successor(index);
}
keys[index] = key;
values[index] = value;
++size;
}
public int[] get(long key) {
int index = indexFor(key);
int count = countHits(key, index);
int[] hits = new int[count];
int hitIndex = 0;
while (keys[index] != NULL) {
if (keys[index] == key) {
hits[hitIndex] = values[index];
++hitIndex;
}
index = successor(index);
}
return hits;
}
private int countHits(long key, int index) {
int numHits = 0;
while (keys[index] != NULL) {
if (keys[index] == key) {
++numHits;
}
index = successor(index);
}
return numHits;
}
private int indexFor(long key) {
return Math.abs((int) ((key * 5700357409661598721L) % keys.length));
}
private int successor(int index) {
return (index + 1) % keys.length;
}
public int size() {
return size;
}
public void load() {
try {
FileChannel channel2 = new RandomAccessFile(str1, "r").getChannel();
MappedByteBuffer mbb2 = channel2.map(FileChannel.MapMode.READ_ONLY, 0, channel2.size());
mbb2.order(ByteOrder.nativeOrder());
assert mbb2.remaining() == savenum * 8;
for (int i = 0; i < savenum; i++) {
long l = mbb2.getLong();
keys[i] = l;
}
channel2.close();
FileChannel channel3 = new RandomAccessFile(str2, "r").getChannel();
MappedByteBuffer mbb3 = channel3.map(FileChannel.MapMode.READ_ONLY, 0, channel3.size());
mbb3.order(ByteOrder.nativeOrder());
assert mbb3.remaining() == savenum * 4;
for (int i = 0; i < savenum; i++) {
int l1 = mbb3.getInt();
values[i] = l1;
}
channel3.close();
} catch (Exception e) {
System.out.println(e);
}
}
public void save() {
try {
FileChannel channel = new RandomAccessFile(str1, "rw").getChannel();
MappedByteBuffer mbb = channel.map(FileChannel.MapMode.READ_WRITE, 0, savenum * 8);
mbb.order(ByteOrder.nativeOrder());
for (int i = 0; i < savenum; i++) {
mbb.putLong(keys[i]);
}
channel.close();
FileChannel channel1 = new RandomAccessFile(str2, "rw").getChannel();
MappedByteBuffer mbb1 = channel1.map(FileChannel.MapMode.READ_WRITE, 0, savenum * 4);
mbb1.order(ByteOrder.nativeOrder());
for (int i = 0; i < savenum; i++) {
mbb1.putInt(values[i]);
}
channel1.close();
} catch (Exception e) {
System.out.println("IOException : " + e);
}
}
}
