If you use a module with two different pathes ( usiing symlinks for instance) does mod_perl knows it's the same code and avoids compiling it twice ?

mod_perl is perl, the way `use' works does not change under mod_perl (perldoc -f use).

It sounds to me like you need to read more about mod_perl.

update: consider this

use strict;
use lib 'blinky';
use Data::Dumper;
warn Dumper( \%INC, \@INC );

__END__
$VAR1 = {
          'Carp.pm' => 'C:/Perl/lib/Carp.pm',
          'Exporter.pm' => 'C:/Perl/lib/Exporter.pm',
          'XSLoader.pm' => 'C:/Perl/lib/XSLoader.pm',
          'strict.pm' => 'C:/Perl/lib/strict.pm',
          'warnings/register.pm' => 'C:/Perl/lib/warnings/register.pm'
+,
          'Config.pm' => 'C:/Perl/lib/Config.pm',
          'warnings.pm' => 'C:/Perl/lib/warnings.pm',
          'lib.pm' => 'C:/Perl/lib/lib.pm',
          'overload.pm' => 'C:/Perl/lib/overload.pm',
          'Data/Dumper.pm' => 'C:/Perl/lib/Data/Dumper.pm'
        };
$VAR2 = [
          'blinky',
          'C:/Perl/lib',
          'C:/Perl/site/lib',
          '.'
        ];
[download]

Try reading perlfaq8 What's the difference between require and use?

MJD says "you can't just make shit up and expect the computer to know what you mean, retardo!"

I run a Win32 PPM repository for perl 5.6.x and 5.8.x -- I take requests (README).

** The third rule of perl club is a statement of fact: pod is sexy.