What resources exist for Database performance-tuning? [closed]

Oracle's very own Tom Kyte has a fantastic repository on every type of performance problem imaginable on http://asktom.oracle.com. He usually takes the time to recreate specific problems and gives very detailed explanations.


This guy's answer to a not-the-same-inquiry is probably a good start.

Hidden Features of MySQL


And something for PostgreSQL: "Performance Optimization" at the official wiki.