The answer is to partition by ingestion time and cluster by device ID. This design minimizes query costs for time-series sensor data because partitioning by ingestion time allows the query engine to perform partition pruning, reading only the partitions covering the last hour, while clustering by device ID further narrows the scan to the specific device’s data within those partitions, drastically reducing the bytes and files scanned. On the Google Professional Cloud Database Engineer exam, this scenario tests your understanding of how BigQuery’s physical storage optimization directly impacts cost and performance for high-frequency streaming data; a common trap is choosing only clustering or only partitioning, which fails to eliminate unnecessary data reads. Remember the memory tip: “Time trims the partitions, device narrows the rows”—ingestion time cuts the time window, and device ID clusters the relevant records inside it.
PCDE Practice Question: Define data structures and implement SQL for Business Intelligence
This PCDE practice question tests your understanding of define data structures and implement sql for business intelligence. 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 data engineer needs to design a table to store time-series sensor data arriving every second. The data will be queried mainly for the last hour over a specific device. Which table design minimizes query costs?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Partition by ingestion_time, cluster by device_id
Option D minimizes query costs because partitioning by ingestion_time allows the query engine to skip partitions outside the last hour, while clustering by device_id further narrows the scan to only the relevant device's data within those partitions. This combination reduces the amount of data read and the number of files scanned, which is critical for high-frequency time-series data.
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.
✗
Partition by ingestion_time, cluster by timestamp
Why it's wrong here
Clustering on timestamp is redundant; the partition column already provides time pruning.
✗
Partition by ingestion_time, no clustering
Why it's wrong here
Without clustering, queries filtering by device_id still scan all rows in the relevant partitions.
✗
No partitioning, cluster by device_id
Why it's wrong here
Without partitioning, queries for the last hour scan the entire table, even with clustering.
✓
Partition by ingestion_time, cluster by device_id
Why this is correct
Partitioning enables time-range pruning; clustering on device_id speeds up per-device lookups.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that clustering by the same column as partitioning provides extra benefit, but in reality it is redundant and can increase maintenance overhead without improving query performance.
Detailed technical explanation
How to think about this question
Under the hood, partitioning creates separate storage containers (e.g., directories or shards) for each time range, enabling partition pruning at the metadata level. Clustering physically co-locates rows with the same device_id within each partition, allowing the query engine to skip non-matching blocks via min-max statistics or bloom filters. In real-world deployments, this design can reduce query latency from minutes to seconds for high-ingestion-rate IoT workloads.
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 startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
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.
Define data structures and implement SQL for Business Intelligence — This question tests Define data structures and implement SQL for Business Intelligence — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Partition by ingestion_time, cluster by device_id — Option D minimizes query costs because partitioning by ingestion_time allows the query engine to skip partitions outside the last hour, while clustering by device_id further narrows the scan to only the relevant device's data within those partitions. This combination reduces the amount of data read and the number of files scanned, which is critical for high-frequency time-series data.
What should I do if I get this PCDE 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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This PCDE 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 PCDE exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.