- A
Keep the auto-increment key but use bit-reversal
Why wrong: Bit-reversal can help but Spanner doesn't support bit-reversal natively; using UUID is simpler.
- B
Use a composite primary key with a hash prefix followed by the UUID
Hash prefix distributes writes evenly; UUID part preserves uniqueness and allows ordering.
- C
Use the UUID as the primary key and create a secondary index on the original integer
Why wrong: Secondary indexes can also become hotspots if monotonically increasing.
- D
Use a monotonically increasing custom ID and rely on Spanner's split management
Why wrong: Monotonically increasing keys cause hotspots; Spanner splits may not avoid this.
Question 79 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.
A team is migrating a MySQL OLTP database to Cloud Spanner. The existing schema uses auto-increment primary keys. They plan to convert them to STRING columns with UUIDs. However, the application also relies on ORDER BY on the original integer key. How should they preserve ordering while avoiding hotspots in Spanner?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"primary"Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
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 a composite primary key with a hash prefix followed by the UUID
To avoid hotspots, the leading part of the primary key should be a hash prefix. To preserve ordering, you can use a composite key where the first part is a hash bucket (e.g., mod 100) and the second part is the UUID. This distributes writes while allowing ordering by the UUID (though not strictly sequential). Another option is to use a monotonically increasing key but with a salt, but that still may cause hotspots. The best practice is to use a hash prefix. The correct answer is to prepend a hash of the UUID as the first key column.
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.
- ✗
Keep the auto-increment key but use bit-reversal
Why it's wrong here
Bit-reversal can help but Spanner doesn't support bit-reversal natively; using UUID is simpler.
- ✓
Use a composite primary key with a hash prefix followed by the UUID
Why this is correct
Hash prefix distributes writes evenly; UUID part preserves uniqueness and allows ordering.
Clue confirmation
The clue word "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use the UUID as the primary key and create a secondary index on the original integer
Why it's wrong here
Secondary indexes can also become hotspots if monotonically increasing.
- ✗
Use a monotonically increasing custom ID and rely on Spanner's split management
Why it's wrong here
Monotonically increasing keys cause hotspots; Spanner splits may not avoid this.
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 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 a composite primary key with a hash prefix followed by the UUID — To avoid hotspots, the leading part of the primary key should be a hash prefix. To preserve ordering, you can use a composite key where the first part is a hash bucket (e.g., mod 100) and the second part is the UUID. This distributes writes while allowing ordering by the UUID (though not strictly sequential). Another option is to use a monotonically increasing key but with a salt, but that still may cause hotspots. The best practice is to use a hash prefix. The correct answer is to prepend a hash of the UUID as the first key column.
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: "primary". Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
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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