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ACE Practice Question: Designing an application that needs to process…
This ACE practice question tests your understanding of designing an application that needs to process…. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
You are designing an application that needs to process exactly once each message published to a topic, even if the consumer fails partway through and restarts. Which GCP service provides built-in exactly-once processing semantics with Pub/Sub?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Best answer
Dataflow with Pub/Sub as the source using the Beam SDK.
Dataflow's Beam runner provides exactly-once processing semantics over Pub/Sub by checkpointing and deduplicating based on message IDs.
B
Distractor review
BigQuery Subscriptions connected directly to the Pub/Sub topic.
BigQuery subscriptions write Pub/Sub messages to BigQuery tables with at-least-once semantics; they don't guarantee exactly-once processing.
C
Distractor review
Cloud Run with a Pub/Sub push subscription and database deduplication table.
Deduplication in Cloud Run requires custom application logic; it's not a built-in infrastructure guarantee and adds application complexity.
D
Distractor review
Cloud Functions subscribed to the Pub/Sub topic with idempotent logic.
Cloud Functions with Pub/Sub get at-least-once delivery. Idempotency helps but doesn't provide exactly-once guarantees at the infrastructure level.
Common exam trap
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Technical deep dive
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
- Use explanations to understand the rule behind the answer.
TExam Day Tips
- Underline the problem statement mentally.
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Related practice questions
Related ACE practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
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Question 3
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Question 4
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Question 5
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Question 6
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FAQ
Questions learners often ask
What does this ACE question test?
Read the scenario before looking for a memorised answer.
What is the correct answer to this question?
The correct answer is: Dataflow with Pub/Sub as the source using the Beam SDK. — Dataflow (Apache Beam) provides exactly-once processing semantics when reading from Pub/Sub. Dataflow checkpoints progress and deduplicates messages using Pub/Sub message IDs, ensuring each record is processed exactly once even through failures and retarts. Pub/Sub alone provides at-least-once delivery; exactly-once requires a downstream processing layer like Dataflow.
What should I do if I get this ACE question wrong?
Identify which ACE exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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This ACE 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 ACE exam.