- A
The primary key is monotonically increasing
Why wrong: The primary key is a UUID, which is not monotonically increasing, so this is not the cause.
- B
The table is not interleaved
Why wrong: Interleaving affects read performance and storage locality, not write hotspotting directly.
- C
The number of Spanner nodes is insufficient
Insufficient Spanner nodes can cause all writes to be handled by a single node if the splits are not distributed, leading to hotspotting.
- D
Secondary indexes are not defined
Why wrong: Secondary indexes are for read queries and do not directly cause write hotspotting.
Question 123 of 999
Design Scalable and Highly Available Cloud Database Solutions →mediumMultiple ChoiceObjective-mapped
PCD Spanner write hotspotting Practice Question
This PCD practice question tests your understanding of design scalable and highly available cloud database solutions. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: spanner write hotspotting. 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.
You are designing a Cloud Spanner schema for a global user profile table. The primary key is a UUID generated client-side. Users report high write latency and hotspotting on a specific node. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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
✓
The number of Spanner nodes is insufficient
While a UUID is generally random and should distribute writes across Spanner splits, if the number of Spanner nodes is insufficient relative to the write load, all writes may be concentrated on a few nodes, causing hotspotting on a specific node. In Spanner, each node serves a set of splits, and with insufficient nodes, multiple splits map to the same node, leading to a bottleneck. This is the most likely cause given the use of a random UUID primary key.
Key principle: Spanner write hotspotting
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The primary key is monotonically increasing
Why it's wrong here
The primary key is a UUID, which is not monotonically increasing, so this is not the cause.
- ✗
The table is not interleaved
Why it's wrong here
Interleaving affects read performance and storage locality, not write hotspotting directly.
- ✓
The number of Spanner nodes is insufficient
Why this is correct
Insufficient Spanner nodes can cause all writes to be handled by a single node if the splits are not distributed, leading to hotspotting.
Clue confirmation
The clue words "most likely", "primary" in the question point toward this answer.
Related concept
Spanner write hotspotting
- ✗
Secondary indexes are not defined
Why it's wrong here
Secondary indexes are for read queries and do not directly cause write hotspotting.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Candidates often assume that any hotspotting is due to monotonically increasing keys, but with a UUID key, it's more likely a resource constraint issue.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- Spanner write hotspotting
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
Spanner write hotspotting
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.
Review spanner write hotspotting, then practise related PCD questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this PCD question test?
Design Scalable and Highly Available Cloud Database Solutions — This question tests Design Scalable and Highly Available Cloud Database Solutions — Spanner write hotspotting.
What is the correct answer to this question?
The correct answer is: The number of Spanner nodes is insufficient — While a UUID is generally random and should distribute writes across Spanner splits, if the number of Spanner nodes is insufficient relative to the write load, all writes may be concentrated on a few nodes, causing hotspotting on a specific node. In Spanner, each node serves a set of splits, and with insufficient nodes, multiple splits map to the same node, leading to a bottleneck. This is the most likely cause given the use of a random UUID primary key.
What should I do if I get this PCD question wrong?
Review spanner write hotspotting, then practise related PCD questions on the same topic to reinforce the concept.
Are there clue words in this question I should notice?
Yes — watch for: "most likely", "primary". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Spanner write hotspotting
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Last reviewed: Jul 4, 2026
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