Ask HN: Custom logging for web applications

I have an application (written in Django) that needs to log lots of data (visitor stats from a Flash app, a url is pinged whenever users do certain things). I've rolled by own logging system along with a library for extracting statistics from the logged data based on the map/reduce pattern. However, I'm having performance problems with my initial quick and dirty implementation (in the stats generation, not in the logging bit yet). This seems like a problem that must have been solved plenty of times before. What do people use for this sort of stuff?