In case you want to learn more about what Perl is exactly doing when accessing hashes, the source code would be one place to start (in particular hv.c).

If you're more interested in a general discussion, you could try Bob Jenkins' site — there are some interesting reads to be found, e.g. Hash Functions for Hash Table Lookup   (probably best to start with the latter, and then dig into the code once you have a clearer idea of what you're looking for).