From: David Masover <ninja@...>
Date: 2009-09-23T10:19:48+09:00
Subject: Re: File.exists? performance

On Tuesday 22 September 2009 11:34:59 am Marcelo Barbudas wrote:
> > How CPU intensive is File.exists? ?
>
> I think I should have said I/O.

It depends entirely what you're doing.

But for what you're talking about, it really can't be much. Think of it this 
way: How many images are you talking about? If your server has anything close 
to a decent amount of RAM, all of those are going to be cached. You're already 
doing FAR more than checking if a file exists (basically a stat(2) call, by my 
count it's going to be at most 52 _bytes_) than you will if you have to 
actually read that image. Worst case, when someone only does a HEAD on an 
image, you'll be doing two stat calls, so it'll be about half the usual speed.

In other words, do what Axel Etzold suggested -- or better yet, don't worry 
about it. Do it this way, and rethink your architecture (or add some sort of 
caching) if it becomes a problem.