- A
Use salting (hash prefix) to distribute writes
Why wrong: Salting would break the natural ordering needed for prefix scans by device_id.
- B
Use field promotion: put device_id as the first component of the row key
Field promotion ensures that queries for all readings of a device can use a prefix scan.
- C
Use a reverse timestamp (e.g., MAX_TIMESTAMP - timestamp) as part of the row key
Reverse timestamp brings the most recent data to the top, making 'latest reading' queries fast via a limit scan.
- D
Use a monotonically increasing timestamp as the first part of the row key
Why wrong: This would cause hotspots and make recent data inefficient to query.
- E
Store the entire row as a single column family to reduce overhead
Why wrong: Column families are for organization, not for optimizing read patterns.
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.
A company is designing a Cloud Bigtable schema for time-series data. The data is written by millions of devices every second. The query patterns are: (1) retrieve the most recent reading for a specific device, (2) retrieve all readings for a device in a time range. Which TWO row key design techniques should the team use to optimize for these patterns? (Choose two.)
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 field promotion: put device_id as the first component of the row key
Using a reverse timestamp allows the most recent data to be at the beginning of the row key, making scans for the latest reading efficient. Field promotion ensures that device_id comes first in the row key, enabling efficient prefix scans for all readings of a device. Salting is not needed because device_id already distributes writes if there are many devices.
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 salting (hash prefix) to distribute writes
Why it's wrong here
Salting would break the natural ordering needed for prefix scans by device_id.
- ✓
Use field promotion: put device_id as the first component of the row key
Why this is correct
Field promotion ensures that queries for all readings of a device can use a prefix scan.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
Use a reverse timestamp (e.g., MAX_TIMESTAMP - timestamp) as part of the row key
Why this is correct
Reverse timestamp brings the most recent data to the top, making 'latest reading' queries fast via a limit scan.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use a monotonically increasing timestamp as the first part of the row key
Why it's wrong here
This would cause hotspots and make recent data inefficient to query.
- ✗
Store the entire row as a single column family to reduce overhead
Why it's wrong here
Column families are for organization, not for optimizing read patterns.
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 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 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: Use field promotion: put device_id as the first component of the row key — Using a reverse timestamp allows the most recent data to be at the beginning of the row key, making scans for the latest reading efficient. Field promotion ensures that device_id comes first in the row key, enabling efficient prefix scans for all readings of a device. Salting is not needed because device_id already distributes writes if there are many devices.
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.
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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