The correct first action is to enable pg_stat_statements and check the query's execution statistics. This extension captures granular metrics like total time, calls, rows processed, and I/O per query, which directly addresses the need to diagnose slow queries in Cloud SQL for PostgreSQL. Without these statistics, you are guessing at why a previously fast query now shows a sequential scan and high CPU—data growth or a plan change could be the culprit, and pg_stat_statements reveals exactly how many rows are being read and where time is spent. On the Google Professional Cloud Database Engineer exam, this scenario tests your ability to follow a methodical diagnostic workflow rather than jumping to index creation or parameter tuning, which are common traps. Remember that pg_stat_statements is the first tool for any unexplained performance regression because it provides the evidence needed before making changes. A useful memory tip: "Stats before steps"—always gather execution statistics before taking corrective action.
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 database engineer for an e-commerce platform running on Cloud SQL for PostgreSQL. The application team reports that a critical report query taking 5 seconds last week now takes over 30 seconds. The database CPU usage has increased from 40% to 85%. The query plan shows a sequential scan on the orders table. Which action should you take first to diagnose the problem?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable pg_stat_statements and check the query's execution statistics.
Option D is correct because enabling pg_stat_statements provides detailed execution statistics (e.g., total time, calls, rows, I/O) for each query, allowing you to identify the root cause of the performance regression without making speculative changes. Since the query plan shows a sequential scan and CPU is high, pg_stat_statements can reveal if the query is now reading more rows due to data growth or plan changes, guiding the next action (e.g., adding an index or tuning parameters).
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.
✗
Migrate the database to Cloud Spanner for better scaling.
Why it's wrong here
Overly aggressive and costly; not a first diagnostic step.
✗
Add a composite index on the orders table based on the query's WHERE clause.
Why it's wrong here
Should only be done after analyzing the query plan and identifying missing indexes.
✗
Increase the machine type to add more vCPUs.
Why it's wrong here
Increases cost and does not address the underlying query performance issue.
✓
Enable pg_stat_statements and check the query's execution statistics.
Why this is correct
Provides necessary metrics to diagnose the query performance degradation.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the principle of 'diagnose before you treat' — the trap here is that candidates jump to adding an index (Option B) or scaling resources (Option C) without first gathering evidence, which is a common mistake in performance troubleshooting.
Detailed technical explanation
How to think about this question
pg_stat_statements is a PostgreSQL extension that tracks query execution metrics like total_time, blk_read_time, and rows, which can be queried from the pg_stat_statements view. In Cloud SQL, it is enabled by default but may require the flag cloudsql.enable_pg_stat_statements to be set; analyzing the query's execution frequency and average time can reveal if the sequential scan is due to outdated statistics (requiring ANALYZE) or a missing index. A real-world scenario is when a table grows beyond a threshold where PostgreSQL's planner switches from an index scan to a sequential scan because it estimates the index is no longer selective enough.
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
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.
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: Enable pg_stat_statements and check the query's execution statistics. — Option D is correct because enabling pg_stat_statements provides detailed execution statistics (e.g., total time, calls, rows, I/O) for each query, allowing you to identify the root cause of the performance regression without making speculative changes. Since the query plan shows a sequential scan and CPU is high, pg_stat_statements can reveal if the query is now reading more rows due to data growth or plan changes, guiding the next action (e.g., adding an index or tuning parameters).
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.
Are there clue words in this question I should notice?
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
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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