The correct answer is to create a clone of the instance, run the update on the clone, then promote it. This approach allows you to run a heavy update on Cloud SQL PostgreSQL without impacting production by isolating the resource-intensive operation in a separate environment. The clone is a fully functional copy of the source instance, so the 10-million-row update can execute without competing for the 8 vCPUs and 30 GB memory of the production database, preventing performance degradation. On the Google Professional Cloud Database Engineer exam, this scenario tests your understanding of Cloud SQL’s point-in-time recovery and cloning features as a safe, one-time data correction strategy. A common trap is attempting to use read replicas or batch processing, but those still affect the primary instance or require complex rollback logic. Remember the memory tip: “Clone, correct, promote” — think of it as a surgical swap rather than a live surgery.
PCDE Plan and manage database infrastructure Practice Question
This PCDE practice question tests your understanding of plan and manage database infrastructure. 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.
Your team uses Cloud SQL for PostgreSQL and needs to run a one-time data correction query that will update 10 million rows. The instance has 8 vCPUs and 30 GB memory. The query is currently running for hours and impacting production performance. What should you do?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a clone of the instance, run the update on the clone, then promote it.
Option B is correct because creating a clone of the Cloud SQL instance provides an isolated environment where the heavy UPDATE can run without impacting production performance. After the update completes on the clone, you can promote it to become the new primary instance, effectively applying the data correction with minimal downtime. This approach avoids the performance degradation caused by running the query on the production instance and leverages Cloud SQL's cloning feature for a one-time data correction.
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.
✗
Create a read replica and run the update on the replica.
Why it's wrong here
Read replicas are read-only; cannot perform updates.
✓
Create a clone of the instance, run the update on the clone, then promote it.
Why this is correct
Cloning provides an isolated environment for the update.
Related concept
Read the scenario before looking for a memorised answer.
✗
Run the query during off-peak hours with reduced concurrency.
Why it's wrong here
Still affects production performance during execution.
✗
Increase the instance size to 16 vCPUs and 60 GB memory before running the query.
Why it's wrong here
This still impacts production during the query.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that read replicas can handle write operations, but in Cloud SQL for PostgreSQL, replicas are strictly read-only and cannot be used for UPDATE queries.
Detailed technical explanation
How to think about this question
Cloud SQL for PostgreSQL uses PostgreSQL's MVCC (Multiversion Concurrency Control) to handle concurrent transactions, but a large UPDATE on 10 million rows generates significant WAL (Write-Ahead Log) traffic and can cause autovacuum pressure, leading to bloat and degraded query performance. Cloning in Cloud SQL creates a full, writable copy of the instance using snapshot technology, which is efficient and does not require additional storage until data changes are made. Promoting the clone after the update is a controlled process that can be done with minimal downtime by redirecting application traffic, making it ideal for one-time data correction tasks.
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.
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: Create a clone of the instance, run the update on the clone, then promote it. — Option B is correct because creating a clone of the Cloud SQL instance provides an isolated environment where the heavy UPDATE can run without impacting production performance. After the update completes on the clone, you can promote it to become the new primary instance, effectively applying the data correction with minimal downtime. This approach avoids the performance degradation caused by running the query on the production instance and leverages Cloud SQL's cloning feature for a one-time data correction.
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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Question Discussion
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