Blatant self-promotion, but people interested in PostgreSQL query processing might also be interested in these slide decks:<p>"Query Execution Techniques in PostgreSQL" <a href="http://neilconway.org/talks/executor.pdf" rel="nofollow">http://neilconway.org/talks/executor.pdf</a><p>"Inside the PostgreSQL Query Optimizer" <a href="http://neilconway.org/talks/optimizer/optimizer.pdf" rel="nofollow">http://neilconway.org/talks/optimizer/optimizer.pdf</a>