PCDE Design and implement database schemas Practice Question
This PCDE practice question tests your understanding of design and implement database schemas. 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 global e-commerce company is designing a Cloud Spanner schema for order processing. They need strong consistency across regions and high write throughput. Orders are identified by a globally unique order ID (UUID). Currently, they use the UUID as the primary key, but they observe write hotspots during peak hours. What primary key design change should they make to distribute writes more evenly?
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 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 starting with a hash of the order ID, followed by the order ID.
Option C is correct because a composite key starting with a high-cardinality column (like a hash of the order ID or a timestamp-partitioned column) distributes writes across multiple splits, avoiding hotspots. Option A (UUID) can cause hotspots if inserted in order; Option B (sequential integers) causes hotspots on the last split; Option D (monotonically increasing timestamp) causes similar hotspot issues.
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 the timestamp of order creation as the primary key.
Why it's wrong here
A monotonically increasing timestamp concentrates writes on a single split, causing hotspots.
✗
Use a sequential integer primary key with auto-increment.
Why it's wrong here
Sequential integers concentrate writes on the last split, causing hotspots.
✓
Use a composite primary key starting with a hash of the order ID, followed by the order ID.
Why this is correct
A hash prefix ensures writes are distributed across all splits, avoiding hotspots.
Clue confirmation
The clue word "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Keep UUID as primary key but add a secondary index on a hash of the UUID.
Why it's wrong here
Adding an index does not change the primary key write distribution; the primary key still causes hotspots.
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 PCDE 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.
Design and implement database schemas — This question tests Design and implement database schemas — 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 starting with a hash of the order ID, followed by the order ID. — Option C is correct because a composite key starting with a high-cardinality column (like a hash of the order ID or a timestamp-partitioned column) distributes writes across multiple splits, avoiding hotspots. Option A (UUID) can cause hotspots if inserted in order; Option B (sequential integers) causes hotspots on the last split; Option D (monotonically increasing timestamp) causes similar hotspot issues.
What should I do if I get this PCDE question wrong?
Identify which PCDE 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.
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Question Discussion
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