The correct choice is to redesign the primary key to avoid monotonic increases, as this directly addresses the root cause of Cloud Spanner hot spots. When primary keys are monotonically increasing—like timestamps or auto-incrementing integers—all new writes land on the same split, overloading a few nodes while others remain underutilized, which explains why CPU is low yet writes are throttled. This scenario tests your understanding of Cloud Spanner’s split architecture and the critical importance of primary key design to distribute writes evenly across nodes, a frequent pain point on the Google Professional Cloud Database Engineer exam. A common trap is assuming that adding nodes or read replicas will fix write bottlenecks, but the real issue is lock contention on hot splits, not overall capacity. Remember the mnemonic: “Monotonic keys cause monotonic pain—hash your keys to spread the rain.”
PCDE Plan and manage database infrastructure Practice Question
This PCDE practice question tests your understanding of plan and manage database infrastructure. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 uses Cloud Spanner with a multi-region configuration (nam3) for a global application. They notice that write latency has increased significantly during peak hours. After investigation, they find that the number of splits has increased from 10 to 50, and the CPU utilization on most nodes is below 10%. However, writes are being throttled due to excessive hot spots on a few nodes. What should they do?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Redesign the primary key to avoid monotonic increases
Option C is correct because hot spots in Spanner are often caused by monotonically increasing primary keys, which concentrate writes on a few splits. Redesigning the key to distribute writes (e.g., using a hash prefix) spreads the load evenly. Option A (increase nodes) does not fix the hot spot; the bottleneck is lock contention on specific splits. Option B (interleaved tables) helps with child table joins but not with primary key distribution. Option D (read replicas) is for read scaling, not write throughput.
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.
✓
Redesign the primary key to avoid monotonic increases
Why this is correct
Using a non-monotonic key (e.g., hashed or UUID) spreads writes across all splits, reducing hot spots and throttling.
Related concept
Read the scenario before looking for a memorised answer.
✗
Enable interleaved tables
Why it's wrong here
Interleaved tables improve locality for related data but do not address the primary key hot spot issue.
✗
Increase the number of nodes
Why it's wrong here
Adding nodes distributes load across more splits but does not eliminate hot spots if the key design causes contention on a few splits.
✗
Use a read replica
Why it's wrong here
Read replicas offload read traffic but do not improve write performance or reduce hot spots.
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.
Plan and manage database infrastructure — This question tests Plan and manage database infrastructure — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Redesign the primary key to avoid monotonic increases — Option C is correct because hot spots in Spanner are often caused by monotonically increasing primary keys, which concentrate writes on a few splits. Redesigning the key to distribute writes (e.g., using a hash prefix) spreads the load evenly. Option A (increase nodes) does not fix the hot spot; the bottleneck is lock contention on specific splits. Option B (interleaved tables) helps with child table joins but not with primary key distribution. Option D (read replicas) is for read scaling, not write throughput.
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.
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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