Output shows these are same.

This warning is important warning: too few iterations for a reliable count

You never actually benchmark with_keys or with_each, you benchmark their return values intead

Consider 

#!/usr/bin/perl --
use strict;
use warnings;

{
    use Benchmark;
    print "##########\n";
    print scalar gmtime, "\n";
    print "perl $] \n";
    for my $iterKeys ( [ -3, 100_000], [ 10, 1_000_000 ] ){
        my $count = $iterKeys->[1];
        my %hash = map { $_ => !!0 } 0 .. $count;
        print "count $count\n";
        Benchmark::cmpthese(
$iterKeys->[0],
{
    for_keys => sub {
        for my $k( keys %hash ){
        }
        return;
    },
    while_each => sub {
        while( my($k,$v) = each %hash ){
        }
        return;
    },
},
        );
        print "\n";
    }
    print "\n";
    print scalar gmtime, "\n";
    print "\n";
        
} 

__END__
##########
Fri Nov 11 08:45:57 2011
perl 5.014001 
count 100000
             Rate while_each   for_keys
while_each 6.08/s         --       -62%
for_keys   16.2/s       166%         --

count 1000000
           s/iter while_each   for_keys
while_each   1.85         --       -59%
for_keys    0.761       143%         --


Fri Nov 11 08:47:19 2011

[download]

I didn't test past 1 million keys, my machine is ancient, and I didn't feel like swapping, but you can observe a trend -- throwing memory at the problem (for_keys) is faster while it fits in ram, but it will eventually reverse

In reply to Re^6: Finding the size of a nested hash in a HoH by Anonymous Monk
in thread Finding the size of a nested hash in a HoH by Jeri

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