The Accidental CartesianSpark · easy · ~8 minA refactor touched the attribution job last night. It normally finishes in 9 minutes; it's been running for 3 hours, shuffle write is 40x normal, and the output row count preview looks... astronomical. The diff was 'just renaming some columns'.Read the plan, find the classic bug.Evidence

Plan & Diff

Numbers

Checkpoints

What happened?

The tell you can use in ANY future incident?

Beyond fixing the condition, what guards stop this class from reaching prod again? Interview-style.