Offloading Reporting Queries with Read Replicas
A gaming company uses Amazon RDS for PostgreSQL to store player profiles and game state data. The database is currently 500 GB and grows by 10 GB per day. The company runs weekly reports that scan the entire database, causing high I/O and CPU usage. The application experiences read latency spikes during report generation. The team wants to minimize performance impact on the application while maintaining the ability to run reports. Which solution should the team implement?
Quick Answer
The answer is to create a read replica and direct all report queries to it. This solution is correct because offloading reporting queries to RDS read replicas eliminates the I/O and CPU contention on the primary database, which directly resolves the read latency spikes the application experiences during report generation. On the AWS Certified Database Specialty DBS-C01 exam, this scenario tests your understanding of read replica use cases for separating analytic workloads from transactional traffic, with a common trap being the temptation to scale up the primary instance instead—which only masks the contention rather than removing it. Remember that read replicas are asynchronous, so they provide near-real-time data without impacting the source database’s performance. A useful memory tip: “Reports go to replicas, writes stay with the primary.”
⚠ Common exam trap
Candidates often confuse Multi-AZ standby instances with read replicas, mistakenly believing the standby can be used for read traffic, but AWS explicitly prevents read access to the standby to maintain synchronous replication integrity.
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 a read replica and direct all report queries to the read replica.
Creating a read replica for Amazon RDS for PostgreSQL allows the team to offload all report queries to a separate read-only endpoint, eliminating the I/O and CPU contention on the primary database. This directly addresses the read latency spikes during report generation without requiring any application changes beyond redirecting the reporting queries. The read replica asynchronously replicates data from the primary instance, ensuring the reports see a near-real-time snapshot of the data while the primary remains dedicated to the application workload.
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 direct all report queries to the read replica.
Why this is correct
A read replica offloads read-intensive workloads from the primary, reducing latency for the application.
- ✗
Enable Multi-AZ deployment to provide a standby instance for failover and use it for reporting.
Why it's wrong here
Multi-AZ standby cannot be used for read queries; it is only for failover.
- ✗
Scale up the RDS instance to a larger instance type to handle the additional load from reports.
Why it's wrong here
Scaling up increases capacity but does not isolate reporting workload; the application may still experience latency.
- ✗
Archive historical game state data to Amazon S3 and delete it from the database to reduce size.
Why it's wrong here
Archiving reduces future growth but does not help with current report performance.
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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 gaming company uses Amazon RDS for PostgreSQL to store player profiles and game state. They report slow queries during peak hours. The DB instance is a db.r5.2xlarge with 500 GB gp2 storage. Which design change would MOST improve read performance for the most frequently accessed player profiles?
hard- A.Implement application-level sharding by player ID
- B.Increase provisioned IOPS on the existing volume
- C.Upgrade to a db.r5.4xlarge instance
- ✓ D.Add a read replica in the same AZ
Why D: Adding a read replica in the same Availability Zone (AZ) offloads read traffic from the primary RDS for PostgreSQL instance, directly improving read performance for frequently accessed player profiles during peak hours. Read replicas asynchronously replicate data using PostgreSQL's streaming replication and can serve SELECT queries without impacting the primary instance's write workload or connection limits.
Variation 2. A company runs an online transaction processing (OLTP) workload on Amazon RDS for PostgreSQL. The database has grown to 2 TB and the company needs to run complex analytical queries that join multiple large tables. These analytical queries are slowing down the OLTP operations. What is the MOST cost-effective solution to separate the workloads?
easy- ✓ A.Create an RDS for PostgreSQL read replica and route analytical queries to it.
- B.Use Amazon ElastiCache for caching analytical query results.
- C.Migrate the analytical queries to Amazon Redshift.
- D.Migrate the OLTP workload to Amazon DynamoDB.
Why A: Creating an RDS for PostgreSQL read replica is the most cost-effective solution because it offloads analytical queries to a separate read-only instance without requiring a full database migration. The read replica uses PostgreSQL's native streaming replication to maintain near-real-time data consistency, allowing complex joins on large tables without competing for the primary instance's I/O and CPU resources. This approach minimizes operational overhead and cost compared to migrating to a separate analytics platform like Redshift.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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