- A
Queries by conversation will be slow.
Why wrong: Queries by conversation prefix are efficient; the issue is write distribution.
- B
Writes will be concentrated on a single split causing hotspots.
Monotonically increasing keys lead to hotspots in Spanner.
- C
The table cannot be interleaved with another table.
Why wrong: Interleaving is still possible.
- D
The table will not support secondary indexes.
Why wrong: Spanner supports secondary indexes regardless of primary key design.
Question 523 of 1,000
PCDOE Design and Plan Database Solutions Practice Question
This PCDOE practice question tests your understanding of design and plan database solutions. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
An engineer is designing a Cloud Spanner schema for a chat application where users send messages. Messages are ordered by timestamp per conversation. The primary key chosen is (ConversationId, MessageId) where MessageId is a monotonically increasing integer. What potential issue might arise with this key design?
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
✓
Writes will be concentrated on a single split causing hotspots.
Option B is correct because using a monotonically increasing integer as the second part of the primary key (MessageId) in Cloud Spanner causes all new writes to be concentrated on a single split (tablet) that handles the highest key range. This creates a hotspot, degrading write throughput and latency, as Cloud Spanner splits data by key range and sequential inserts target the same node.
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.
- ✗
Queries by conversation will be slow.
Why it's wrong here
Queries by conversation prefix are efficient; the issue is write distribution.
- ✓
Writes will be concentrated on a single split causing hotspots.
Why this is correct
Monotonically increasing keys lead to hotspots in Spanner.
Clue confirmation
The clue word "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The table cannot be interleaved with another table.
Why it's wrong here
Interleaving is still possible.
- ✗
The table will not support secondary indexes.
Why it's wrong here
Spanner supports secondary indexes regardless of primary key design.
Common exam traps
Common exam trap: answer the scenario, not the keyword
In Google Cloud Spanner, monotonically increasing keys cause write hotspots because Spanner splits data by key range and sequential inserts target the same tablet, unlike traditional single-node databases where such keys are safe.
Detailed technical explanation
How to think about this question
Cloud Spanner splits data into tablets based on key ranges, and each tablet is served by a specific node. A monotonically increasing MessageId causes all new rows to be written to the last tablet, creating a write hotspot that can saturate that node's resources. To avoid this, use a key design that distributes writes, such as a hash prefix or a UUID-based MessageId, ensuring load is spread across splits.
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.
TExam Day Tips
- 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 exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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: Writes will be concentrated on a single split causing hotspots. — Option B is correct because using a monotonically increasing integer as the second part of the primary key (MessageId) in Cloud Spanner causes all new writes to be concentrated on a single split (tablet) that handles the highest key range. This creates a hotspot, degrading write throughput and latency, as Cloud Spanner splits data by key range and sequential inserts target the same node.
What should I do if I get this PCDOE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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