PDE Designing Data Processing Systems Practice Question
A team wants to use Cloud Pub/Sub Lite for a high-throughput, low-cost messaging system. They need exactly-once delivery to subscribers. What should they know about Pub/Sub Lite's delivery guarantees?
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
✓
Pub/Sub Lite provides at-least-once delivery, same as standard Pub/Sub.
Pub/Sub Lite offers at-least-once delivery like standard Pub/Sub; exactly-once is not guaranteed.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Pub/Sub Lite provides at-least-once delivery, same as standard Pub/Sub.
Why this is correct
Pub/Sub Lite guarantees at-least-once delivery, so duplicate messages can reach subscribers; exactly-once is unavailable. This satisfies the stem's constraint by clarifying that the team cannot rely on deduplication, and must implement idempotent processing or their own deduplication logic to achieve exactly-once semantics.
- ✗
Pub/Sub Lite provides exactly-once delivery when using push subscriptions.
Why it's wrong here
Pub/Sub Lite offers at-least-once delivery only; exactly-once is not provided by any subscription type, push or pull. It is tempting because standard Pub/Sub supports exactly-once with pull subscriptions, but Lite trades that guarantee for lower cost, so subscribers must handle duplicates themselves.
- ✗
Pub/Sub Lite provides exactly-once delivery when using pull subscriptions.
Why it's wrong here
Pub/Sub Lite offers at-least-once delivery on pull subscriptions, so duplicates can reach subscribers; exactly-once is not a Lite guarantee. It tempts because standard Pub/Sub pull subscriptions do provide exactly-once delivery within a region, which is the correct choice when that guarantee is mandatory.
- ✗
Pub/Sub Lite supports exactly-once delivery by default.
Why it's wrong here
Pub/Sub Lite delivers at-least-once by default, so duplicate messages can arrive; exactly-once requires explicit handling and is not the default. It tempts because standard Pub/Sub supports exactly-once delivery, making it the right service when that guarantee is required.
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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.