The answer is to monitor the "Row count returned by index" and "Statement scan rows returned" metrics. These two Cloud Monitoring metrics directly validate whether secondary indexes are being used efficiently in Cloud Spanner. The "Statement scan rows returned" metric reveals the total number of rows scanned per query; when this number is significantly higher than the actual rows returned, it indicates that the query is performing a full table scan or using an overly broad index, rather than leveraging a targeted secondary index. The "Row count returned by index" metric shows how many rows are returned specifically from index scans; if this count is high but the final result set is small, the index is likely too broad or not selective enough. On the Google Professional Cloud Database Engineer exam, this question tests your ability to distinguish between metrics that measure index efficiency versus general performance indicators like latency or CPU. A common trap is confusing overall query latency with index-specific behavior. Memory tip: think "scanned vs. returned" — if scanned rows dwarf returned rows, your index is not doing its job.
PCDE Monitor and optimize database performance Practice Question
This PCDE practice question tests your understanding of monitor and optimize database performance. 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.
You are a Cloud Database Engineer managing a Cloud Spanner instance. You notice that some queries are taking longer than expected. You suspect that the queries are not using secondary indexes efficiently. Which TWO metrics should you monitor in Cloud Monitoring to validate your suspicion? (Choose two.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Statement scan rows returned
Option B: 'Statement scan rows returned' shows the number of rows scanned per query; a high value compared to rows returned indicates inefficient index usage. Option D: 'Row count returned by index' shows how many rows are returned from index scans; if it's high but the final result is small, the index may be too broad. Option A is about overall latency, not specific to index usage. Option C is about CPU, not directly about index usage. Option E is about lock conflicts, unrelated.
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.
✗
CPU utilization
Why it's wrong here
CPU utilization is a general metric, not specific to index usage.
✓
Statement scan rows returned
Why this is correct
High scan rows vs. rows returned indicates inefficient index usage.
Related concept
Read the scenario before looking for a memorised answer.
✗
Lock conflicts
Why it's wrong here
Lock conflicts indicate concurrency issues, not index efficiency.
✓
Row count returned by index
Why this is correct
This metric helps determine if the index is returning too many rows.
Related concept
Read the scenario before looking for a memorised answer.
✗
Query scan latency (mean)
Why it's wrong here
This metric shows overall scan latency, not specifically index efficiency.
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.
Trap categories for this question
Command / output trap
This metric shows overall scan latency, not specifically index efficiency.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
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.
Monitor and optimize database performance — This question tests Monitor and optimize database performance — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Statement scan rows returned — Option B: 'Statement scan rows returned' shows the number of rows scanned per query; a high value compared to rows returned indicates inefficient index usage. Option D: 'Row count returned by index' shows how many rows are returned from index scans; if it's high but the final result is small, the index may be too broad. Option A is about overall latency, not specific to index usage. Option C is about CPU, not directly about index usage. Option E is about lock conflicts, unrelated.
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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