Top 3 Backfill Interview Questions
Browse 3 real-world technical and behavioral interview questions about Backfill. Review scenarios, edge cases, and architectural best practices.
Events for a daily revenue table arrive up to three days late. How do you design the pipeline and the backfill?
Land raw events unchanged by arrival date, then rebuild each revenue day from that raw layer by event date. Each run overwrites only the days its new arrivals touched, a day is provisional until the three-day window closes, and the backfill is the same job run over a date range, never a separate script.
A transform has been writing wrong revenue figures for three days and six downstream tables have consumed it. How do you backfill the corrected data without double-counting anything?
Make the write idempotent before you make it correct: partition-level replace rather than append, so rerunning a day produces the same result whether it runs once or five times. Then work out how far the contamination spread, because a downstream table that accumulated rather than recomputed will not fix itself when the source is repaired.
How would you design a data pipeline you can safely re-run?
Design a safely rerunnable data pipeline by making each output partition a deterministic result of its input partition, overwriting instead of appending, and writing into idempotent sinks that tolerate retries and late events.