Question 144 of 1,663
RDS Read Replicas for Reporting Workloads
A company runs a reporting application that queries an Amazon RDS for PostgreSQL database. The queries are complex and take a long time to run, causing performance degradation on the primary instance. The team wants to improve query performance without affecting the transactional workload. Which solution should they use?
Quick Answer
The answer is to create one or more RDS read replicas and direct reporting queries to them. This solution offloads reporting queries from the primary PostgreSQL instance, eliminating performance degradation on transactional workloads by routing complex, long-running SELECT statements to a separate read-only copy. On the AWS Certified Database Specialty DBS-C01 exam, this scenario tests your understanding of read replica use cases versus scaling up or switching to Aurora—a common trap is choosing a larger instance size, which helps throughput but doesn’t isolate reporting load and is less cost-effective. Remember that read replicas are ideal for read-heavy workloads like reporting, analytics, or BI, and they can be promoted to primary for disaster recovery. Memory tip: “Replicas for reads, primary for deeds”—keep transactional writes on the primary and offload all reporting reads to replicas.
⚠ Common exam trap
Test-takers frequently assume scaling up the primary instance (Option A) is the simplest fix, but the exam tests the understanding that workload isolation via read replicas is the correct architectural pattern for separating reporting from transactional workloads.
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
✓
Create one or more read replicas and direct reporting queries to them
Amazon RDS read replicas allow you to offload read-heavy reporting queries from the primary PostgreSQL instance. By directing complex, long-running queries to one or more read replicas, you eliminate resource contention on the primary instance, preserving transactional workload performance. RDS for PostgreSQL supports up to 15 read replicas, which can be promoted to a primary instance if needed, and they use asynchronous replication to stay nearly current.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Increase the instance size of the primary database
Why it's wrong here
Scaling up helps both workloads but is not the best separation.
- ✓
Create one or more read replicas and direct reporting queries to them
Why this is correct
Read replicas offload read traffic, isolating reporting queries from transactional workload.
- ✗
Migrate to Amazon RDS for MySQL and use Multi-AZ
Why it's wrong here
Multi-AZ is for high availability, not for offloading read queries.
- ✗
Use Amazon ElastiCache to cache the results of complex queries
Why it's wrong here
Caching works for repeated queries but not for ad-hoc complex queries.
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Same concept, more angles
2 more ways this is tested on DBS-C01
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company uses Amazon RDS for PostgreSQL to run a reporting application. The reporting queries are complex and take several minutes to complete, causing performance impact on the primary instance. The company wants to isolate the reporting workload without data staleness. Which solution should they implement?
medium- A.Implement an Amazon ElastiCache cluster to cache query results.
- B.Enable Multi-AZ and use the standby instance for reporting.
- C.Take a manual snapshot of the database and restore it for reporting.
- ✓ D.Create a read replica and direct reporting queries to it.
Why D: Creating a read replica of the Amazon RDS for PostgreSQL primary instance allows you to offload complex reporting queries to the replica without impacting the primary. Read replicas use asynchronous replication (based on PostgreSQL streaming replication), which provides near-real-time data with minimal staleness, satisfying the requirement to isolate the reporting workload without significant data staleness.
Variation 2. A social media application stores user posts in an Amazon RDS for PostgreSQL instance. The application experiences a sudden spike in read traffic during peak hours, causing database bottlenecks. The team needs to improve read scalability without changing the application code. Which solution is MOST cost-effective?
hard- A.Migrate to Amazon DynamoDB with DAX
- B.Enable Multi-AZ on the RDS instance
- ✓ C.Use Amazon RDS for PostgreSQL Read Replicas
- D.Use Amazon ElastiCache to cache query results
Why C: Amazon RDS for PostgreSQL Read Replicas allow you to offload read traffic from the primary DB instance to one or more read-only replicas, improving read scalability without any application code changes. This is the most cost-effective solution as it leverages the existing PostgreSQL engine and requires only minimal additional compute and storage costs for the replicas.
Last reviewed: Jul 4, 2026
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