- A
Use Cloud Storage triggers with event filters and configure the function to delete the file after successful processing
Why wrong: Cloud Storage triggers are at-least-once, and deleting the file after processing may still cause duplicates if the function fails before deletion.
- B
Use Cloud Pub/Sub to store file notification events and use Dataflow for processing with exactly-once guarantees
Dataflow provides exactly-once processing semantics when used with Pub/Sub.
- C
Use Cloud Tasks to queue file processing tasks and configure retries with deduplication
Why wrong: Cloud Tasks can deduplicate tasks, but the function processing the task needs to be idempotent to guarantee exactly-once.
- D
Use Cloud Workflows to orchestrate the pipeline and use idempotent writes to BigQuery
Why wrong: Idempotent writes help but do not guarantee exactly-once processing if the function is retried.
Quick Answer
The answer is to use Cloud Pub/Sub to store file notification events and Dataflow for processing with exactly-once guarantees. This approach works because Pub/Sub provides reliable, ordered event delivery, while Dataflow’s built-in exactly-once processing semantics ensure that each file is processed precisely once, even if a worker fails and retries—eliminating duplicates through checkpointing and transactional writes to BigQuery. On the Google Professional Cloud Developer exam, this scenario tests your understanding of how to combine managed services to achieve end-to-end data integrity, a common pitfall being the assumption that Cloud Storage triggers (which are at-least-once) or Cloud Tasks (which require idempotent processing) can guarantee exactly-once. A key memory tip: think of Pub/Sub as the “reliable event bus” and Dataflow as the “exactly-once engine”—together they form the only native Google Cloud pair that enforces this guarantee without custom deduplication logic.
PCD Integrating Google Cloud services Practice Question
This PCD practice question tests your understanding of integrating google cloud services. 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.
A team is designing a data pipeline that uses Cloud Storage for input files, Cloud Functions to process each file, and writes results to BigQuery. The pipeline must guarantee exactly-once processing of each file, even if the function fails and retries. Which approach should the team take?
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
Use Cloud Pub/Sub to store file notification events and use Dataflow for processing with exactly-once guarantees
Option B is correct because using Cloud Pub/Sub to store file notification events and Dataflow for processing provides exactly-once guarantees. Option A may lead to duplicates because Cloud Storage triggers are at-least-once. Option C with Cloud Tasks can deduplicate tasks but processing may still be at-least-once if not idempotent. Option D with Cloud Workflows does not inherently provide exactly-once.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 Cloud Storage triggers with event filters and configure the function to delete the file after successful processing
Why it's wrong here
Cloud Storage triggers are at-least-once, and deleting the file after processing may still cause duplicates if the function fails before deletion.
- ✓
Use Cloud Pub/Sub to store file notification events and use Dataflow for processing with exactly-once guarantees
Why this is correct
Dataflow provides exactly-once processing semantics when used with Pub/Sub.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use Cloud Tasks to queue file processing tasks and configure retries with deduplication
Why it's wrong here
Cloud Tasks can deduplicate tasks, but the function processing the task needs to be idempotent to guarantee exactly-once.
- ✗
Use Cloud Workflows to orchestrate the pipeline and use idempotent writes to BigQuery
Why it's wrong here
Idempotent writes help but do not guarantee exactly-once processing if the function is retried.
Common exam traps
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.
Detailed technical explanation
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.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Identify which PCD 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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Integrating Google Cloud services — study guide chapter
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FAQ
Questions learners often ask
What does this PCD question test?
Integrating Google Cloud services — This question tests Integrating Google Cloud services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use Cloud Pub/Sub to store file notification events and use Dataflow for processing with exactly-once guarantees — Option B is correct because using Cloud Pub/Sub to store file notification events and Dataflow for processing provides exactly-once guarantees. Option A may lead to duplicates because Cloud Storage triggers are at-least-once. Option C with Cloud Tasks can deduplicate tasks but processing may still be at-least-once if not idempotent. Option D with Cloud Workflows does not inherently provide exactly-once.
What should I do if I get this PCD question wrong?
Identify which PCD 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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
This PCD 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 PCD exam.
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