Why should Celery tasks be idempotent, and what is acks_late?
PICTURE THIS: DATA SPLIT
Fit on train, tune on val, report on test once.
Simple meaning
Workers can crash after running a task but before ack, so the broker redelivers.
WHY — Celery instead of guessing?
Why interviewers care about Celery:
on Celery.
the situation, the default choice, and one exception - that reads as experience.
Name the idea, why it exists, then one short example.
End with when you use it and one common pitfall.
STEPS — What happens step by step?
Before you speak the answer, walk the interviewer through these steps:
- 1Workers can crash after
running a task but before ack, so the broker redelivers.
- 2Idempotent tasks (unique constraints,
upserts) make that safe.
- 3acks_late acknowledges after the
task returns, reducing loss at the cost of at-least-once delivery.
- 4Give an example
One tiny concrete case you can say aloud.
- 5Common mistake
What juniors usually get wrong.
- 6Close
When you pick this over the alternative.
EXAMPLE — See it in action
Here's a short line you can speak, broken into clear beats:
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
Workers can crash after running a task but before ack, so the broker redelivers. Idempotent tasks (unique constraints, upserts) make that safe.