Quick Answer
The answer is to add read replicas, as this is the most effective optimization for reducing CPU load on Cloud SQL for PostgreSQL during read-heavy peaks. By directing SELECT traffic to replicas, you offload the primary instance from processing these queries, which directly lowers its CPU utilization and preserves resources for writes and critical operations. On the Google Professional Cloud Database Engineer exam, this scenario tests your understanding of horizontal read scaling versus vertical scaling or caching—a common trap is choosing to increase machine size, which only masks the problem without addressing the root cause of read contention. Remember the memory tip: “Replicas read, primary writes,” so when you see high CPU from read-heavy workloads, think replicas first, not bigger hardware.
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.
A company has a Cloud SQL for PostgreSQL instance that experiences high CPU usage during peak hours due to read-heavy queries. Which optimization is most effective for reducing CPU load?
Use connection pooling
Why wrong: Connection pooling reduces overhead but not the CPU cost of query execution.
Increase memory size
Why wrong: More memory can help caching but does not directly reduce query processing CPU.
Add read replicas
Read replicas distribute read queries, reducing CPU on the primary instance.
Enable automatic storage increase
Why wrong: Automatic storage increase addresses storage capacity, not CPU load.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Add read replicas
Adding read replicas offloads read-heavy queries from the primary Cloud SQL for PostgreSQL instance, distributing the query load and reducing CPU utilization on the primary. This is the most direct and effective optimization for read-heavy workloads because replicas handle SELECT traffic while the primary focuses on writes and critical operations.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Use connection pooling
Why it's wrong here
Connection pooling reduces overhead but not the CPU cost of query execution.
Increase memory size
Why it's wrong here
More memory can help caching but does not directly reduce query processing CPU.
Add read replicas
Why this is correct
Read replicas distribute read queries, reducing CPU on the primary instance.
Related concept
Read the scenario before looking for a memorised answer.
Enable automatic storage increase
Why it's wrong here
Automatic storage increase addresses storage capacity, not CPU load.
Common exam traps
Google Cloud often tests the misconception that connection pooling or memory increases are universal performance fixes, but for read-heavy CPU spikes, offloading reads to replicas is the targeted solution.
Detailed technical explanation
Cloud SQL read replicas use PostgreSQL's streaming replication (WAL-based) to maintain an almost real-time copy of the primary database. When read replicas are configured, applications can route SELECT queries to the replica's endpoint, which has its own CPU and memory resources, thereby isolating the primary from read load. In a real-world scenario, a reporting dashboard hitting the primary with complex aggregations could be redirected to a replica, reducing primary CPU from 95% to 30% without any query changes.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
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FAQ
Monitor and optimize database performance — This question tests Monitor and optimize database performance — Read the scenario before looking for a memorised answer..
The correct answer is: Add read replicas — Adding read replicas offloads read-heavy queries from the primary Cloud SQL for PostgreSQL instance, distributing the query load and reducing CPU utilization on the primary. This is the most direct and effective optimization for read-heavy workloads because replicas handle SELECT traffic while the primary focuses on writes and critical operations.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Same concept, more angles
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Variation 1. You are monitoring a Cloud SQL for PostgreSQL instance and notice that the CPU utilization is consistently above 90% during peak hours. What is the most cost-effective initial action to reduce CPU load?
easyWhy C: Adding a read replica is the most cost-effective initial action because it offloads read queries from the primary instance, reducing CPU contention without incurring the cost of upgrading the entire instance. Cloud SQL for PostgreSQL replicas use native streaming replication, so they handle read traffic while the primary focuses on writes, directly addressing high CPU utilization from read-heavy workloads.
Last reviewed: Jun 30, 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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