I've done one format which was append-only (so a pretty easy problem to solve) on one homogeneous system with metadata that had above-average performance (compa

I've done one format which was append-only (so a pretty easy problem to solve) on one homogeneous system with metadata that had above-average performance (compared to the commercial and open-source alternatives available at the time) but it sounds you have me well-beaten. These are the war-stories that I love to hear. What was your problem domain, what were the recurring implementation problems, where were the bugs primarily?