The bug was the timezone. The bug is always the timezone.

The report said the report was empty. Not wrong, not late — empty, for one customer, on one day of the month, and only if you asked before lunch.

I want to write the rest of this properly, because the shape of the failure was more interesting than the fix. For now, the summary is that we stored a date, called it a day, and it was in fact an instant, and an instant belongs to somewhere.

The six betrayals

1. A date that is really a timestamp.
2. A timestamp with no zone attached.
3. A zone attached at write time but not at read time.
4. Midnight, which happens twice a year in some places and never in others.
5. A database that helpfully converts, and a client that helpfully converts again.
6. Me, assuming any of the above had been handled.

More soon, once I’ve stopped being annoyed about it.