On-disk MergeSort Numbers and code

gistfile1.java

import java.io.File;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorCompletionService;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

import org.apache.hadoop.io.IntWritable;

import de.jungblut.datastructure.Merger;
import de.jungblut.datastructure.SortedFile;

public class SpillSortTimer {

  public static void main(String[] args) throws Exception {
    final int availableProcessors = Runtime.getRuntime().availableProcessors();
    final ExecutorService pool = Executors
        .newFixedThreadPool(availableProcessors);
    final ExecutorCompletionService<File> service = new ExecutorCompletionService<>(
        pool);
    long numBytes = (1000 * 1000 * 1000);
    // sort 1gb of data
    final int numInts = (int) (numBytes / 4) / availableProcessors;
    System.out.println("Writing and sorting " + numBytes + " bytes as "
        + numBytes / 4 + " integers with " + availableProcessors + " threads.");
    long start = System.currentTimeMillis();
    for (int i = 0; i < availableProcessors; i++) {
      final int x = i;
      service.submit(new Callable<File>() {
        @Override
        public File call() throws Exception {
          String outPath = "/tmp/merged_" + x + ".bin";
          try (SortedFile<IntWritable> ints = new SortedFile<>(
              "/tmp/merge_sorted_" + x, outPath, 16 * 1000 * 1000,
              IntWritable.class, true)) {
            IntWritable intWritable = new IntWritable();
            Random r = new Random();
            for (int i = 0; i < numInts; i++) {
              intWritable.set(r.nextInt());
              ints.collect(intWritable);
            }
          }
          return new File(outPath);
        }
      });
    }
    List<File> files = new ArrayList<>();
    for (int i = 0; i < availableProcessors; i++) {
      files.add(service.take().get());
    }
    System.out.println("Merging " + files.size() + " sorted segments after "
        + (System.currentTimeMillis() - start) / 1000 + "s.");
    // merging the files
    Merger.<IntWritable> merge(IntWritable.class, new File(
        "/tmp/final_merge_output.bin"), files);

    long taken = System.currentTimeMillis() - start;
    System.out.println("Took " + (taken / 1000) + "s to mergesort overall "
        + numBytes + " bytes.");

    pool.shutdownNow();
  }
}

gistfile2.txt

Writing and sorting 1000000000 bytes as 250000000 integers with 8 threads.
Starting intermediate merge of 9 files.
Starting intermediate merge of 9 files.
Starting intermediate merge of 9 files.
Starting intermediate merge of 9 files.
Starting intermediate merge of 9 files.
Starting intermediate merge of 9 files.
Starting intermediate merge of 9 files.
Starting intermediate merge of 9 files.
Merging 8 sorted segments after 74s.
Took 98s to mergesort overall 1000000000 bytes.