Why Writing a File Cost Such a Memory?

Question

As a test case I tried the next code on my Mac OS X 10.2.3:
import java.io.*;
public class WriteZero {          
public static void main(String[] args) throws Exception{
java.io.BufferedOutputStream bs = new java.io.BufferedOutputStream(new FileOutputStream("zeros"));
int mb=1024*1024;
int mb500 = mb*500;
try{
  int k=0;
    while((1==1)){
         bs.write(0x0);
         k++;
       if(k%mb==0){
            Thread.sleep(200);//inessential but enables to work in the back ground
            System.gc();// tries to free memory
        }else if(k>mb500) break;//50mb
}catch(InterruptedException ie){;
}catch(java.lang.Throwable th){
    System.err.println(th.toString());
}finally{
     if(bs!=null) bs.close();
}This simply writes the size of 500MB of the characters '\u0000.' In the course of writing the free RAM decreases monotonously until it reaches around 6 MB of free memory, recording 919 pageouts. The number 919 of pageouts is very rare on my OS, which has 512MB of RAM. What causes this consumption of memory in simple writing a file?

Answer 1

Something up with either your VM or VM configuration maybe? I just copied and pasted your code, and it's cruising at just under 6MB - which means maybe 2 MB allocated in heap space.
Verbose:gc indicates that full garbage collections are being done about every second, but that the heap is a stable size.
Check your max and min heap-sizes, and also try it on a different VM if you can - there's no reason for this program to blow up memory that way. Also should be no need to call GC at all.