Linux /dev/shm (Shared memory file system) write performance test

FileOutTest.java

package linuxfs;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.channels.FileChannel;

/*
* Author: Ashwin Jayaprakash
*/
public class FileOutTest {
    public static void main(String[] args) throws Exception {
        for (int i = 0; i < 25; i++) {
            testOut(args[0]);

            Thread.sleep(500);
        }
    }

    private static void testOut(String fileName) throws IOException {
        long startTime = System.nanoTime();
        long lengthBytes = testWrite(fileName);
        long endTime = System.nanoTime();

        System.out.printf("Finished writing [%d] bytes in [%d] millis%n", lengthBytes, (endTime - startTime) / 1000000);
    }

    private static long testWrite(String arg) throws IOException {
        File file = new File(arg);
        file.delete();
        file.createNewFile();

        FileOutputStream fos = new FileOutputStream(file);
        FileChannel fileChannel = fos.getChannel();

        for (int i = 0; i < 1024; i++) {
            long number = System.nanoTime();

            for (int j = 0; j < 8; j++) {
                fos.write(Long.toString(number).getBytes());
                number++;
            }

            if (i % 128 == 0) {
                fileChannel.force(true);

                System.out.printf(" Current length [%d] bytes%n", file.length());
            }
        }

        fos.close();

        return file.length();
    }
}

FileOutTest.log

cloudera@cloudera-demo:~/shm-tests$ javac linuxfs/*.java

cloudera@cloudera-demo:~/shm-tests$ java -cp . linuxfs.FileOutTest /dev/shm/outtest.txt | grep Finished
Finished writing [114688] bytes in [153] millis
Finished writing [114688] bytes in [70] millis
Finished writing [114688] bytes in [61] millis
Finished writing [114688] bytes in [62] millis
Finished writing [114688] bytes in [61] millis
Finished writing [114688] bytes in [62] millis
Finished writing [114688] bytes in [59] millis
Finished writing [114688] bytes in [54] millis
Finished writing [114688] bytes in [52] millis
Finished writing [114688] bytes in [50] millis
Finished writing [114688] bytes in [52] millis
Finished writing [114688] bytes in [51] millis
Finished writing [114688] bytes in [49] millis
Finished writing [114688] bytes in [53] millis
Finished writing [114688] bytes in [55] millis
Finished writing [114688] bytes in [49] millis
Finished writing [114688] bytes in [56] millis
Finished writing [114688] bytes in [50] millis
Finished writing [114688] bytes in [51] millis
Finished writing [114688] bytes in [51] millis
Finished writing [114688] bytes in [52] millis
Finished writing [114688] bytes in [50] millis
Finished writing [114688] bytes in [51] millis
Finished writing [114688] bytes in [49] millis
Finished writing [114688] bytes in [51] millis

cloudera@cloudera-demo:~/shm-tests$ ls -lh /dev/shm/
total 372K
-rw-r--r-- 1 cloudera cloudera 112K 2011-03-03 02:09 outtest.txt
.. .. 

cloudera@cloudera-demo:~/shm-tests$ df -h /dev/shm/
Filesystem            Size  Used Avail Use% Mounted on
none                  502M  372K  501M   1% /dev/shm

cloudera@cloudera-demo:~/shm-tests$ mount -l
/dev/sda1 on / type ext4 (rw,errors=remount-ro)
...
none on /dev type devtmpfs (rw,mode=0755)
none on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620)
none on /dev/shm type tmpfs (rw,nosuid,nodev)
...

cloudera@cloudera-demo:~/shm-tests$ java -cp . linuxfs.FileOutTest /tmp/outtest.txt | grep Finished
Finished writing [114688] bytes in [565] millis
Finished writing [114688] bytes in [450] millis
Finished writing [114688] bytes in [461] millis
Finished writing [114688] bytes in [392] millis
Finished writing [114688] bytes in [482] millis
Finished writing [114688] bytes in [485] millis
Finished writing [114688] bytes in [399] millis
Finished writing [114688] bytes in [375] millis
Finished writing [114688] bytes in [376] millis
Finished writing [114688] bytes in [363] millis
Finished writing [114688] bytes in [390] millis
Finished writing [114688] bytes in [301] millis
Finished writing [114688] bytes in [382] millis
Finished writing [114688] bytes in [368] millis
Finished writing [114688] bytes in [372] millis
Finished writing [114688] bytes in [357] millis
Finished writing [114688] bytes in [415] millis
Finished writing [114688] bytes in [455] millis
Finished writing [114688] bytes in [422] millis
Finished writing [114688] bytes in [369] millis
Finished writing [114688] bytes in [431] millis
Finished writing [114688] bytes in [384] millis
Finished writing [114688] bytes in [419] millis
Finished writing [114688] bytes in [407] millis
Finished writing [114688] bytes in [309] millis

cloudera@cloudera-demo:~/tomcat-native$ ls -alh /tmp/outtest.txt 
-rw-r--r-- 1 cloudera cloudera 112K 2011-03-03 02:09 /tmp/outtest.txt