hardMultiple ChoiceObjective-mapped
PDE Practice Question: A Dataflow streaming pipeline uses stateful…
A Dataflow streaming pipeline uses stateful transformations with per-key state and timers. After a deployment, the team observes that the pipeline is reprocessing events from the last 30 minutes every time it restarts. The pipeline's checkpoint is configured to persist every 10 seconds. Which change should be made to prevent unnecessary reprocessing?
⚠ Common exam trap
Google Cloud often tests the misconception that increasing checkpoint frequency or changing state backends solves reprocessing issues, when the real solution is idempotent sinks to handle duplicates from replay.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable idempotent writes to the sink by adding a unique identifier per event.
Enabling idempotent writes ensures that even if events are reprocessed due to pipeline restarts, the sink will deduplicate them based on the unique identifier. This prevents duplicate data from being written, which is the core issue when stateful transformations cause reprocessing of events from the last 30 minutes. The checkpoint interval (10 seconds) is already frequent enough; the problem is not checkpoint frequency but the lack of deduplication at the sink.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use a non-volatile state backend like Cloud Bigtable for state storage.
Why it's wrong here
State is already persisted in checkpoint files; the issue is about replay semantics.
- ✗
Increase the checkpoint interval to 60 seconds to reduce frequency of checkpoints.
Why it's wrong here
Longer checkpoint interval increases potential reprocessing window.
- ✓
Enable idempotent writes to the sink by adding a unique identifier per event.
Why this is correct
Idempotent writes prevent duplicates from being written when reprocessing occurs.
- ✗
Decrease the checkpoint interval to 1 second to checkpoint more frequently.
Why it's wrong here
More frequent checkpoints reduce reprocessing window, but not the root cause.
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