timestamp timings

[Hani Suleiman]

I've run this test and listing files is pretty consistently faster than 
opening and reading a file. The list approach becomes slower than the 
file when there are around 20+ files in the directory, so if a solution 
whereby timestamps are put in a dedicated dir is put in place, it's 
consistently faster than reading a file. I'm including my micro 
benchmark inline, so feel free to run it and improve either time ;)

For writing, the stamp-in-name solution is faster (obviously) since 
we're just creating an empty file, vs creating a file and writing into 
it.

Also I think that holding the file open is probably a bad idea, given 
that it'd rule out multiple VM's using the same index.

public class FileTest
{
  static File dir = new File("testdir");
  static class TimestampFileFilter implements FileFilter
  {
    private String name;
    TimestampFileFilter(String name)
    {
      this.name = name;
    }
    public boolean accept(File pathname)
    {
      return pathname.getName().startsWith(name + ".");
    }
  }
  public static long testFileList(String name)
  {
    TimestampFileFilter filter = new TimestampFileFilter(name);
    File[] files = dir.listFiles(filter);
    long latest = 0;
    for(int i = 0; i < files.length; i++)
    {
      File timestampFile = files[i];
      String fileName = timestampFile.getName();
      long timestamp = 
Long.parseLong(fileName.substring(fileName.lastIndexOf('.') + 1));
      if(timestamp > latest) latest = timestamp;
    }
    return latest;
  }

  public static long testReadFile(File file) throws IOException
  {
    FileInputStream fis = new FileInputStream(file);
    DataInputStream dis = new DataInputStream(fis);
    long timestamp = dis.readLong();
    fis.close();
    return timestamp;
  }
  public static void main(String[] args) throws IOException
  {
    dir.mkdir();
    File file = new File(dir, "blah.1234");
    FileOutputStream fos = new FileOutputStream(new File(dir, 
"timestamp"));
    DataOutputStream dos = new DataOutputStream(fos);
    dos.writeLong(System.currentTimeMillis());
    fos.close();
    file.createNewFile();
    long now = System.currentTimeMillis();
    int iterations = 100000;
    for(int i=0;i<iterations;i++)
    {
      testFileList("blah");
    }
    System.out.println("list time=" + 
((double)(System.currentTimeMillis()-now)/iterations) + "ms");
    for(int i = 0; i < iterations; i++)
    {
      testReadFile(new File(dir, "timestamp"));
    }
    System.out.println("read time=" + 
((double)(System.currentTimeMillis() - now) / iterations) + "ms");
  }
}

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