- A
[timestamp reversed]#[sensor_id]
Why wrong: Reversed timestamp still leads to sequential writes; not as effective as hashing.
- B
[sensor_id]#[timestamp]
Why wrong: If sensor_id is sequential (e.g., auto-increment), writes still hotspot. Better to hash sensor_id.
- C
[hash of sensor_id]#[timestamp]
Hashing distributes writes across tablets, avoiding hotspotting.
- D
[timestamp]#[sensor_id]
Why wrong: Timestamp prefix leads to hotspotting as all writes go to same tablet server.
Question 805 of 1,000
PDE Storing the Data Practice Question
This PDE practice question tests your understanding of storing the data. 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 is designing a Bigtable row key for a time-series application that records temperature sensor readings every second. To avoid hotspotting, they want to distribute writes across all nodes. Which row key design is best?
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
✓
[hash of sensor_id]#[timestamp]
Hotspotting occurs when sequential keys hit a single tablet server. A reversed timestamp or hashed prefix distributes writes. Pre-pending a hash ensures even distribution. Timestamp alone causes hotspotting. Sensor ID + timestamp can still be sequential if sensor ID is low cardinality.
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.
- ✗
[timestamp reversed]#[sensor_id]
Why it's wrong here
Reversed timestamp still leads to sequential writes; not as effective as hashing.
- ✗
[sensor_id]#[timestamp]
Why it's wrong here
If sensor_id is sequential (e.g., auto-increment), writes still hotspot. Better to hash sensor_id.
- ✓
[hash of sensor_id]#[timestamp]
Why this is correct
Hashing distributes writes across tablets, avoiding hotspotting.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
[timestamp]#[sensor_id]
Why it's wrong here
Timestamp prefix leads to hotspotting as all writes go to same tablet server.
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 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 PDE 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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Storing the Data — study guide chapter
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Storing the Data practice questions
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FAQ
Questions learners often ask
What does this PDE question test?
Storing the Data — This question tests Storing the Data — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: [hash of sensor_id]#[timestamp] — Hotspotting occurs when sequential keys hit a single tablet server. A reversed timestamp or hashed prefix distributes writes. Pre-pending a hash ensures even distribution. Timestamp alone causes hotspotting. Sensor ID + timestamp can still be sequential if sensor ID is low cardinality.
What should I do if I get this PDE question wrong?
Identify which PDE 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.
About these practice questions
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Last reviewed: Jul 4, 2026
This PDE 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 PDE exam.
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