use Benchmark qw/:all/;

@lrg_hash{ 0 .. 20000 } = ();

@sml_hash{ 0 .. 10 } = ();
$sml_hash{ 5000 } = undef; # Create a hash key of the same name in
                           # %sml_hash as in %lrg_hash.

cmpthese (  500000, {
            Big     => '$lrg_hash{5000}=1;',
            Little  => '$sml_hash{5000}=1;'
} );

__OUTPUT__
           Rate    Big Little
Big    378788/s     --    -1%
Little 381679/s     1%     --