#! perl -slw
use strict;
#use Math::Random::MT qw[ rand ];
use Devel::Size qw[ total_size ];

our $S //= 1; srand( $S );

my %hash;
for( 1 .. 1e6 ) {
    my( $x, $y, $z ) = ( int( rand 20 ), int( rand 1.2e6 ), int( rand 1.2e6 ) );
#    ++$hash{ $x }{ $y }{ $z };
#    ++$hash{ join $;, $x, $y, $z };
#    ++$hash{ pack 'Q', $x * 1.2e6**2 + $y * 1.2e6 + $z };
    ++$hash{ unpack 'A6', pack 'Q', $x * 1.2e6**2 + $y * 1.2e6 + $z };
}
print total_size( \%hash ), ' ', scalar keys %hash;

__END__
    ++$hash{ $x }{ $y }{ $z };                                              269 897 378
    ++$hash{ join $;, $x, $y, $z };                                         106 036 953         40%
    ++$hash{ pack 'Q', $x * 1.2e6**2 + $y * 1.2e6 + $z };                    98 388 672         36.5%
    ++$hash{ unpack 'A6', pack 'Q', $x * 1.2e6**2 + $y * 1.2e6 + $z };       96 193 539         35.6%

##</code><code>##

C:\test>perl -E"say join ' ', int( rand 20 ), sort{ $a<=>$b } int( rand 1.2e6 ), int( rand 1.2e6 ) for 1 .. 1e6" 
| sort 
| perl -nle"if($last eq $_){ ++$n }else{ print qq[$last : $n];$n=1} $last=$_" 
| wc -l
 999978