File.exists? performance

Hi.

How CPU intensive is File.exists? ?

I am thinking of adding theme support in my rails project. I want it to
check if theme image exists and if it doesn’t display a default one.

This would mean a File.exists? for each image_tag call.

How CPU intensive is File.exists? ?

I think I should have said I/O.

-------- Original-Nachricht --------

Datum: Wed, 23 Sep 2009 01:34:59 +0900
Von: Marcelo B. [email protected]
An: [email protected]
Betreff: Re: File.exists? performance

How CPU intensive is File.exists? ?

I think I should have said I/O.


M.

Dear Marcelo,

you might use profiling with,e.g., ruby-prof.

http://on-ruby.blogspot.com/2006/08/profile-and-ruby-prof.html

Best regards,

Axel

On Tuesday 22 September 2009 11:34:59 am Marcelo B. 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 E. 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.

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