mediumMultiple Select
PDE Practice Question: Which TWO features of Cloud Pub/Sub guarantee…
Which TWO features of Cloud Pub/Sub guarantee at-least-once delivery and enable exactly-once processing downstream? (Choose two.)
⚠ Common exam trap
Google Cloud often tests the misconception that message ordering or replay features contribute to delivery guarantees, when in fact ordering is about sequence and replay is not a native Pub/Sub capability; the key trap is confusing 'exactly-once delivery' (which Pub/Sub does not offer) with 'exactly-once processing' (which requires subscriber-side idempotency).
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
✓
Subscriber-retry policy with exponential backoff.
Option A is correct because a subscriber-retry policy with exponential backoff ensures that when a message handler fails or does not acknowledge in time, Pub/Sub redelivers the message with increasing delays, which is a core mechanism supporting at-least-once delivery. Option E is correct because acknowledgment deadlines determine how long Pub/Sub waits for an ack before redelivering, and message persistence (retaining messages in storage until acknowledged or expired) guarantees that messages are not lost, thereby enforcing at-least-once delivery. Together, these features let downstream consumers deduplicate or use idempotent processing to achieve exactly-once processing semantics. Option B is not marked correct because exactly-once delivery is an optional subscription setting, not enabled by default, and the question asks for features guaranteeing at-least-once delivery. Option C is not correct because message ordering by key only preserves order within an ordering key and does not itself guarantee delivery or exactly-once processing. Option D is not correct because Cloud Dataproc integration is unrelated to Pub/Sub delivery guarantees or replay semantics.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Subscriber-retry policy with exponential backoff.
Why this is correct
Retries ensure messages are eventually delivered on failure.
- ✗
Exactly-once delivery subscription setting (optional, not enabled by default)
Why it's wrong here
This ensures that publishers cannot duplicate messages.
- ✗
Message ordering by message key.
Why it's wrong here
Ordering provides FIFO, not delivery guarantees.
- ✗
Cloud Dataproc integration for message replay.
Why it's wrong here
Dataproc is not directly involved in Pub/Sub delivery guarantees.
- ✓
Acknowledgment deadlines and message persistence.
Why this is correct
Messages are stored until acknowledged; deadlines trigger redelivery.
Go deeper
Related to this question
About these practice questions
One of 747 original PDE practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This PDE practice question is part of Courseiva's free Google Cloud certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PDE exam.