I've always wondered what happens at the deeper levels of a DB beyond just SQL-literacy. The memory-management tricks (pages, overflows, pointers and remains techniques etc.) is always a great reminder of low-level abstractions I am blessed to not worry about. True programming seems to lie in the OS...
My company is still using MyISAM, so I know a little bit about its lower-level details.
The good news is that being primitive also means being simple...
Postgres design is very complex at first look, but very greatly designed and meaningful, I very like the way they support table-spaces. Good reading!