Implementing transactions (reference)

I would like to learn some more about how transactions are implemented
in SQL databases, specifically about what goes on behind the scene when
you start a new transactions, do some operations, and finally commit the
operations. In particular, I'd like to understand how the database
programmers make this happen. It seems like every transaction requires a
"parallel reality" for the database until it is finally committed.

Is there some definitive database textbook that addresses this topic
that would help an inquisitive person (and experienced programmer)
understand what's going on behind the scenes? Does PostgreSQL follow the
canonical standard? Where in the code would I start looking to
understand this better?

-Fred