Reduce CPU Load on PostgreSQL with Read Replicas
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?
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.
⚠ Common exam trap
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.
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
✓
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.
Answer analysis
Option-by-option breakdown
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.
- ✗
Enable automatic storage increase
Why it's wrong here
Automatic storage increase addresses storage capacity, not CPU load.
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Same concept, more angles
1 more way this is tested on PCDE
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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?
easy- A.Remove unnecessary indexes to reduce write overhead
- B.Reduce the max_connections parameter to limit concurrent users
- ✓ C.Add a read replica to offload read traffic
- D.Increase the machine type (e.g., go to a higher vCPU count)
Why 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.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.