[ruby-talk:10901] Re: /bin/sh script beats pants off ruby script

greg strockbine ([e-mail]) wrote:
> why is ruby so damn slow?
> 
> I don't understand this.  I rewrote a /bin/sh script in
> ruby and the sh script runs much faster.  I ran the script on 
> both Linux and Solaris.  The script removes a symlink and 
> replaces it with a copy of the linked to file.  

You are essentially matching /bin/cp against ruby's File.syscopy routine
(written in ruby), not sh against ruby.

> The ruby script took 20 seconds and the sh script took 7
> seconds.  I don't remember the file size.   I don't understand
> the difference.  The sh script looks so sloppy.

For what it's worth, I can't quite reproduce your numbers. While ruby is
(naturally, we have some overhead) a bit slower than /bin/cp, it's not
nearly by that much. Remember that when you're working on UNIX,
benchmarking file operations can be extremely tricky. For instance:

* The disk cache is going to throw everything off entirely. If the
  file has been read/copied before, chances are that it is still
  cached in memory, and will take only a fraction of the time to
  read again.

* Conversely, writing the file may be miraculously fast, but unless
  you add a sync right after the last write, you will have zero
  reliable information as to how long _that_ takes.

* Networked filesystems add another huge question mark.

Essentially, to benchmark file system operations, you will have at
the very least to start with a freshly booted system and take a
few precautions to make sure that you actually measure what you
want to measure. And without further information, it's really not
possible to tell exactly what went wrong. As I mentioned above,
I cannot reproduce those discrepancies.

			Reimer Behrends