Sebastian,
Those figures are the time it took to write and read 50MB. So your
results were 23MB/s write and about 250MB/s read.
I've change the program to use NIO just for interests sake and the
results are quite surprising. Firstly, there's really no
improvement at all on the write speed. Perhaps its is being hard
drive limited? Secondly, the reads: using normal IO I get between
80MB/s and 120MB/s. But with NIO the reads drop to between 40MB/s
and 60MB/s. NIO is slower?!
Both tests attached (and updated to show the MB/s as output). BTW,
you may want to clear you /private/tmp directory after this test ;)
Interestingly, I've also learnt a thing or two about Activity
Monitor. It seems the File system cache lives in the blue part of
the pie chart. Each time you run this test, you'll see a chunk of
the green give way to blue. When you run out green, both the write
and read speeds drop. Moving the files to the Trash has no
effect. If you use up all your Free mem (green) then empty the
trash, the blue will virtually dissapear leaving you with a lot of
green. This really has no bearing on anything, it just interested
me so I thought I'd pass it on.
NIO Test
-------------
import java.io.*;
import java.nio.channels.FileChannel;
import java.nio.ByteBuffer;
/**
* Created by IntelliJ IDEA.
* User: brendon
* Date: Jul 29, 2005
* Time: 5:09:55 PM
* To change this template use File | Settings | File Templates.
*/
public class NIOTest {
private static final long testFileSize = 50 * 1024 * 1024;
private static final int BUF_SIZE = 8192;
private static final byte[] chunk = new byte[BUF_SIZE];
private static final double NANO = 1000.0 * 1000.0 * 1000.0;
static {
for (int i = 0; i < chunk.length; i++) {
chunk[i] = (byte) (Math.random() * 255);
}
}
public static void main(String[] args) throws IOException {
File writeFile = File.createTempFile("vmBench", ".writeFile");
FileOutputStream fos = new FileOutputStream(writeFile);
FileChannel writeChannel = fos.getChannel();
long testStart = System.nanoTime();
writeChunkOfData(writeChannel);
long testFinish = System.nanoTime();
System.out.println("Write: " + (50 / ((testFinish -
testStart) / NANO)) + " MB/s");
File readFile = new File(writeFile.getPath());
FileInputStream fis = new FileInputStream(readFile);
FileChannel readChannel = fis.getChannel();
testStart = System.nanoTime();
readChunkOfData(readChannel);
testFinish = System.nanoTime();
System.out.println("Read: " + (50 / ((testFinish -
testStart) / NANO)) + " MB/s");
}
private static void readChunkOfData(FileChannel bis) throws
IOException {
ByteBuffer byteBuffer = ByteBuffer.allocate(8192);
while (bis.read(byteBuffer) != -1) {
byteBuffer.clear();
};
}
private static void writeChunkOfData(FileChannel fileChannel)
throws IOException {
ByteBuffer byteBuffer = ByteBuffer.allocateDirect(BUF_SIZE);
long bytesWritten = 0;
while (bytesWritten < testFileSize) {
int len = (int) Math.min(BUF_SIZE, (testFileSize -
bytesWritten));
byteBuffer.put(chunk, 0, len);
byteBuffer.flip();
bytesWritten += fileChannel.write(byteBuffer);
byteBuffer.clear();
}
}
}
IOTest
-----------
import java.io.*;
public class IOTest {
private static final long testFileSize = 50 * 1024 * 1024;
private static final int BUF_SIZE = 8192;
private static final byte[] chunk = new byte[BUF_SIZE];
private static final double NANO = 1000.0 * 1000.0 * 1000.0;
static {
for (int i = 0; i < chunk.length; i++) {
chunk[i] = (byte) (Math.random() * 255);
}
}
public static void main(String[] args) throws IOException {
File writeFile = File.createTempFile("vmBench", ".writeFile");
FileOutputStream fos = new FileOutputStream(writeFile);
BufferedOutputStream bos = new BufferedOutputStream(fos);
long testStart = System.nanoTime();
writeChunkOfData(bos);
long testFinish = System.nanoTime();
System.out.println("Write: " + (50 / ((testFinish -
testStart) / NANO)) + " MB/s");
File readFile = new File(writeFile.getPath());
FileInputStream fis = new FileInputStream(readFile);
BufferedInputStream bis = new BufferedInputStream(fis);
testStart = System.nanoTime();
readChunkOfData(bis);
testFinish = System.nanoTime();
System.out.println("Read: " + (50 / ((testFinish -
testStart) / NANO)) + " MB/s");
}
private static void readChunkOfData(BufferedInputStream bis)
throws IOException {
byte[] readBuffer = new byte[BUF_SIZE];
while (bis.read(readBuffer) != -1);
}
private static void writeChunkOfData(BufferedOutputStream bos)
throws IOException {
long bytesWritten = 0;
while (bytesWritten < testFileSize) {
int len = (int) Math.min(BUF_SIZE, (testFileSize -
bytesWritten));
bos.write(chunk, 0, len);
bytesWritten += len;
}
bos.flush();
}
}
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