Re: Java vs. Perl file I/O benchmarks; valid test?

A reasonable explanation of why Perl is faster is that you are using the expression

  $file = <FILE>;
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This is going to be handled by an opcode or two, that will run at C speed. On the other hand, the Java implementation is forced to use an explicit loop to fetch all the contents of the file. Other things being equal, this will kill Java.

What does really strike me, though, is the fact that the Java version is about three times as long. In terms of programmer efficiency, that's an important factor to take into consideration. Much more so that raw I/O throughput.

I'm no expert at understanding Perl's op codes, but if you do a perl -MO=Terse copyfile you can get a feeling for what is going on under the hood.

Dwelling on this overnight, it occurred to me that the java implementation is not following the spec "read a file in to a variable". The Perl implementation is slurping the entire file into a variable, which puts considerable effort on the VM manager. The Java implementation, on the other hand, is reading a bit from the input file, and then writing a bit to the output file, until the input file is exhausted.

At no time does the Java version hold an entire copy of the file in core, whereas Perl does, paying the added cost of system overhead while the kernel frantically discards 10 megabytes of pages used for caching and buffering, in order to give them to the Perl process.</>

A fairer comparison would be to use this code:

  open(IN, $ARGV[0]);
  open(OUT, ">$ARGV[1]");
  print OUT <IN>;
  close IN;
  close OUT;
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Looking at it that way, it's clear the Perl programmer would have already typed in the program, corrected spurious syntax errors, run the program, received the results, before the Java programmer had finished typing in the Java program.

print@_{sort keys %_},$/if%_=split//,'= & *a?b:e\f/h^h!j+n,o@o;r$s-t%t#u'

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Re: Re: Java vs. Perl file I/O benchmarks; valid test? by danboo (Beadle) on Mar 01, 2002 at 14:01 UTC
A couple things. I don't see the looping that you're talking about in the java versions. The java version from the original poster provides 2 methods for copying, and both read the whole contents of the file into an array and then write that array out to a new file. So the overall idea is the same: read the entire first file into memory, write that memory to a second file. Also, you do realize that the java "version" is actually 2 different methods? So it's not really as long as it appears. Additionally, condensing the JDK 1.4 version I gave below down to some hideuos anonymous objects it gets pretty short. Not on par with the perl version, but hey, that's one of perl's features. `import java.io.; import java.nio.; import java.nio.channels.*; public class X2 { public static void main (String [] args) throws Exception { FileChannel in = new FileInputStream(args[0]).getChannel(); new FileOutputStream(args[1]).getChannel().write(in.map( FileChannel.MapMode.READ_ONLY, 0, in.size())); } }` [download] Cheers, - danboo	[reply] [d/l]

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Re: Re: Java vs. Perl file I/O benchmarks; valid test?
by danboo (Beadle) on Mar 01, 2002 at 14:01 UTC

Also, you do realize that the java "version" is actually 2 different methods? So it's not really as long as it appears. Additionally, condensing the JDK 1.4 version I gave below down to some hideuos anonymous objects it gets pretty short. Not on par with the perl version, but hey, that's one of perl's features.

import java.io.*;
import java.nio.*;
import java.nio.channels.*;

public class X2 {
  public static void main (String [] args) throws Exception {
    FileChannel in = new FileInputStream(args[0]).getChannel();
    new FileOutputStream(args[1]).getChannel().write(in.map(
      FileChannel.MapMode.READ_ONLY, 0, in.size()));
  }
}
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- danboo

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