This is a story about a problem that took a long time to solve. As in, no one noticed it was a problem for a couple years then it took another year to solve. It involves using the time series database Cassandra, some bad assumptions made by the initial programmers who were more used to relational databases, and a reliance on unit tests that test for a short period of time but miss long term problems. And there is a bonus, somewhat related story at the end.