- A
CPU utilization
Why wrong: CPU utilization is a general metric, not specific to index usage.
- B
Statement scan rows returned
High scan rows vs. rows returned indicates inefficient index usage.
- C
Lock conflicts
Why wrong: Lock conflicts indicate concurrency issues, not index efficiency.
- D
Row count returned by index
This metric helps determine if the index is returning too many rows.
- E
Query scan latency (mean)
Why wrong: This metric shows overall scan latency, not specifically index efficiency.
Question 84 of 1,000
Monitor Cloud Spanner Secondary Index Usage
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.)
Quick Answer
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.
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
✓
Statement scan rows returned
Option B is correct because 'Statement scan rows returned' measures the number of rows scanned by a query, which directly indicates whether a full table scan is occurring instead of an efficient index seek. If this metric is high relative to the rows returned, it confirms that secondary indexes are not being used effectively, leading to longer query times.
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
The trap here is that candidates often confuse general performance metrics like CPU utilization or latency with index-specific metrics, failing to realize that only row-level scan and return metrics directly reveal index usage efficiency.
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
Cloud Spanner uses a distributed storage engine where secondary indexes are stored as separate tables. When a query uses a secondary index, the 'Statement scan rows returned' metric should closely match the number of rows actually returned, whereas a full table scan will show a much larger scan count. Monitoring this metric alongside 'Row count returned by index' (Option D) allows you to compute the scan-to-return ratio; a high ratio indicates that the query is scanning many rows unnecessarily, often due to a missing or misused index.
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 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
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FAQ
Questions learners often ask
What does this PCDE question test?
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 is correct because 'Statement scan rows returned' measures the number of rows scanned by a query, which directly indicates whether a full table scan is occurring instead of an efficient index seek. If this metric is high relative to the rows returned, it confirms that secondary indexes are not being used effectively, leading to longer query times.
What should I do if I get this PCDE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
This PCDE 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 PCDE exam.
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