- A
Row key: deviceID#timestamp
Why wrong: Without salting, sequential timestamps cause hotspotting under high write load.
- B
Row key: (reverseTimestamp#deviceID)
Why wrong: Reverse timestamp first still causes hotspotting because all writes have similar timestamps.
- C
Row key: (hash(deviceID)#deviceID#reverseTimestamp)
Salting distributes writes, deviceID enables filtering, reverseTimestamp orders recent first.
- D
Row key: timestamp#deviceID
Why wrong: Timestamp first causes all writes to go to a single node, creating a hotspot.
Question 436 of 1,000
PCDOE Design and Plan Database Solutions Practice Question
This PCDOE practice question tests your understanding of design and plan database solutions. 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.
You are designing a Bigtable schema for a time-series application that records sensor readings every second. Queries always filter by device ID and time range. To avoid hotspotting and ensure recent data is retrieved quickly, which row key design is MOST effective?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"always"Why it matters: Absolute qualifier. An answer using 'always' is only correct if there are genuinely no exceptions — absolute statements are often wrong in networking.
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
✓
Row key: (hash(deviceID)#deviceID#reverseTimestamp)
Salting (hash prefix) distributes writes across nodes, avoiding hotspots from sequential timestamps. Field promotion (device ID first) allows efficient prefix scans. Reverse timestamp ensures most recent data appears first when scanning.
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.
- ✗
Row key: deviceID#timestamp
Why it's wrong here
Without salting, sequential timestamps cause hotspotting under high write load.
- ✗
Row key: (reverseTimestamp#deviceID)
Why it's wrong here
Reverse timestamp first still causes hotspotting because all writes have similar timestamps.
- ✓
Row key: (hash(deviceID)#deviceID#reverseTimestamp)
Why this is correct
Salting distributes writes, deviceID enables filtering, reverseTimestamp orders recent first.
Clue confirmation
The clue word "always" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Row key: timestamp#deviceID
Why it's wrong here
Timestamp first causes all writes to go to a single node, creating a hotspot.
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.
Trap categories for this question
Similar concept trap
Reverse timestamp first still causes hotspotting because all writes have similar timestamps.
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 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 PCDOE 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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FAQ
Questions learners often ask
What does this PCDOE question test?
Design and Plan Database Solutions — This question tests Design and Plan Database Solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Row key: (hash(deviceID)#deviceID#reverseTimestamp) — Salting (hash prefix) distributes writes across nodes, avoiding hotspots from sequential timestamps. Field promotion (device ID first) allows efficient prefix scans. Reverse timestamp ensures most recent data appears first when scanning.
What should I do if I get this PCDOE question wrong?
Identify which PCDOE 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.
Are there clue words in this question I should notice?
Yes — watch for: "always". Absolute qualifier. An answer using 'always' is only correct if there are genuinely no exceptions — absolute statements are often wrong in networking.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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Last reviewed: Jul 4, 2026
This PCDOE 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 PCDOE exam.
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