I had seen this before, but I can't recommend it enough. I very much like resources like this that explain things by explaining how they are implemented. Once

I had seen this before, but I can't recommend it enough. I very much like resources like this that explain things by explaining how they are implemented. Once you understand the basics of how a database is implemented, a lot of the performance implications of your queries make sense. It also really helps in the understanding of what is going on in EXPLAIN output.