我运行一个 java 代码,它产生大量的读写文本文件。程序源代码非常简单,在一个循环中,我在一个测试文件中写入了 2000 行,然后我再次读取它们,只是为了生成大量的磁盘读写操作。但是当程序运行时,我通过“iostat -d -x 1”监控磁盘,我发现第二个“r/s”的读取没有变化,但“w/s”按我的预期增加了!!! 这是 iostat 命令的示例输出:
Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util
sda 0.00 913.00 0.00 82.00 0.00 7872.00 96.00 0.58 7.09 7.11 58.30
Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util
sda 0.00 869.00 0.00 79.00 0.00 7584.00 96.00 0.57 7.11 7.18 56.70
Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util
sda 0.00 847.00 0.00 77.00 0.00 7392.00 96.00 0.57 7.42 7.43 57.20
Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util
sda 0.00 1221.00 0.00 113.00 0.00 10760.00 95.22 0.84 7.47 7.32 82.70
如图所示,所有“r/s”都为零!但是在Java程序中,我读的和我写的一样多?!当我运行 Java 代码时,每秒写入次数增加,但“r/s”没有变化!这是我在监控磁盘时运行的 java 代码:
import java.io.*;
public class Test {
public static void main(String [] args) throws IOException{
String fileName = "/scratch/dump_file.txt";
File f = new File(fileName);
// Attempt to delete it
boolean success = f.delete();
int j=0;
while(j<20000)
{
++j;
Writer output = null;
String text = "A test content";
File file = new File(fileName);
output = new BufferedWriter(new FileWriter(file));
int i=1;
while(i<2000)
{
//Here we start writing 2000 lines into file line by line
output.write("j==="+Integer.toString(j)+text+Integer.toString(i)+"\n");
++i;
}
output.close();
System.out.println("Your file has been written");
String line = null;
try {
// FileReader reads text files in the default encoding.
FileReader fileReader = new FileReader(fileName);
BufferedReader bufferedReader =
new BufferedReader(fileReader);
i=1;
while((line = bufferedReader.readLine()) != null) {
//Here we start reading from file line by line and show the result on screen
++i;
System.out.println(line);
}
// Always close file
bufferedReader.close();
}
catch(FileNotFoundException ex) {
System.out.println(
"Unable to open file '" +
fileName + "'");
}
catch(IOException ex) {
System.out.println(
"Error reading file '"
+ fileName + "'");
// Or we could just do this:
// ex.printStackTrace();
}
}
}
}