use strict;
use warnings;
use Time::HiRes qw/time/;

my %hash;
my $n = 1000000;
@hash{1..$n} = 1 x $n;

my $s = time();
my @k = keys %hash;
print scalar @k, ": ";
print time()-$s, "\n";

$s = time();
print scalar keys %hash, ": ";
print time()-$s, "\n";