PDE Designing data processing systems Practice Question
This PDE practice question tests your understanding of designing data processing systems. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 company is designing a data processing pipeline for real-time sensor data. They want to ensure low latency and exactly-once processing semantics. Which two Google services should they combine to achieve this? (Choose 2)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Cloud Pub/Sub with exactly-once delivery
Cloud Pub/Sub with exactly-once delivery (Option C) ensures that each message is delivered to subscribers exactly once, preventing duplicates in the pipeline. Cloud Dataflow with exactly-once processing mode (Option D) provides end-to-end exactly-once semantics by leveraging consistent snapshots and idempotent sinks, which is critical for real-time sensor data pipelines requiring low latency and accuracy.
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.
✗
Cloud Dataproc with Spark Streaming
Why it's wrong here
Spark Streaming typically provides at-least-once semantics; exactly-once requires additional complexity.
✗
Cloud Functions with Cloud Pub/Sub triggers
Why it's wrong here
Cloud Functions are at-least-once by default.
✓
Cloud Pub/Sub with exactly-once delivery
Why this is correct
Pub/Sub can be configured for exactly-once delivery to subscribers.
Related concept
Read the scenario before looking for a memorised answer.
Read the scenario before looking for a memorised answer.
✗
Cloud IoT Core with device gateways
Why it's wrong here
IoT Core handles device management, not processing semantics.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that Cloud Pub/Sub alone provides end-to-end exactly-once processing, but candidates must recognize that Pub/Sub only guarantees delivery exactly once to subscribers, while Dataflow is needed to ensure processing exactly once across transformations and sinks.
Detailed technical explanation
How to think about this question
Cloud Dataflow's exactly-once processing mode relies on the 'snapshot' mechanism, which periodically saves the state and progress of each pipeline stage, allowing recovery without duplicates. Cloud Pub/Sub's exactly-once delivery uses a client-assigned message ID and a server-side deduplication window (typically 10 minutes) to prevent duplicate publishes, but subscribers must still handle idempotency for end-to-end guarantees. In practice, combining these services ensures that even if a sensor sends duplicate data due to network retries, the pipeline processes it exactly once, maintaining low latency through streaming rather than micro-batching.
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.
TExam Day Tips
→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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Designing data processing systems — This question tests Designing data processing systems — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Cloud Pub/Sub with exactly-once delivery — Cloud Pub/Sub with exactly-once delivery (Option C) ensures that each message is delivered to subscribers exactly once, preventing duplicates in the pipeline. Cloud Dataflow with exactly-once processing mode (Option D) provides end-to-end exactly-once semantics by leveraging consistent snapshots and idempotent sinks, which is critical for real-time sensor data pipelines requiring low latency and accuracy.
What should I do if I get this PDE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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