Re (tilly) 1: sort performance

You could avoid repeated double-lookups with a Schwartzian sort:

my @sorted_keys = map {$_->[0]}
    sort {$a->[1] cmp $b->[1]}
    map {[$_, $hash{$_}{this}]} keys %hash;
[download]

(Read it bottom to top and it will make more sense.)

This is more memory intensive, but doing the double lookup in the sort block means that it happens O(n * log(n)) times. Doing it in a map means it only happens n times. (Where n is the number of keys.)

In Section Seekers of Perl Wisdom