The correct answer is to migrate to Amazon Aurora with read replicas. This works because Aurora’s distributed storage architecture decouples compute from storage, allowing replicas to apply redo logs asynchronously with far less overhead than the physical replication used by RDS for PostgreSQL. Since all Aurora replicas share the same underlying storage volume, they don’t need to copy and replay full write-ahead logs, which dramatically reduces read replica lag even under heavy write loads during a flash sale, while write performance on the primary remains unaffected. On the AWS Certified Database Specialty DBS-C01 exam, this scenario tests your understanding of Aurora’s log-based replication versus traditional PostgreSQL streaming replication—a common trap is assuming that simply increasing replica instance size will fix lag, when the architectural difference is the key. Remember the mnemonic: “Aurora’s shared storage slashes lag—no log copy, no lag.”
DBS-C01 Workload-Specific Database Design Practice Question
This DBS-C01 practice question tests your understanding of workload-specific database design. 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 runs an e-commerce platform on Amazon RDS for PostgreSQL. During a flash sale, the database experiences high write load and read replicas lag significantly. The application uses read replicas for reporting queries. Which design change would most effectively reduce replica lag without compromising write performance?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Migrate to Amazon Aurora with read replicas.
Option C is correct because Amazon Aurora's distributed storage architecture decouples compute from storage, allowing replicas to apply redo logs with minimal overhead compared to RDS for PostgreSQL's physical replication. Aurora's replicas share the same underlying storage volume, so replica lag is significantly reduced even under heavy write loads, while write performance on the primary remains unaffected due to the asynchronous, log-based replication mechanism.
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.
✗
Increase the instance size of the primary database.
Why it's wrong here
Larger instance may handle write load better but does not directly reduce replica lag.
✗
Add more read replicas to distribute the reporting load.
Why it's wrong here
Adding replicas does not reduce lag per replica; the underlying replication mechanism remains unchanged.
✓
Migrate to Amazon Aurora with read replicas.
Why this is correct
Aurora has faster replication (typically <100ms) and is designed to handle high write loads with minimal replica lag.
Related concept
Read the scenario before looking for a memorised answer.
✗
Convert the RDS instance to a Multi-AZ deployment.
Why it's wrong here
Multi-AZ is for high availability, not for reducing read replica lag.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume adding more replicas or scaling the primary will solve replication lag, but they fail to recognize that the fundamental replication mechanism in RDS for PostgreSQL (streaming WAL) is the bottleneck, whereas Aurora's shared-storage architecture inherently minimizes lag.
Detailed technical explanation
How to think about this question
In Amazon Aurora, the cluster volume is a distributed, SSD-backed virtual storage layer that spans multiple Availability Zones, and replicas connect to the same storage without copying data from the primary. This eliminates the need for physical WAL shipping and replay, reducing replica lag to sub-second levels even during peak writes, whereas RDS for PostgreSQL replicas must stream and apply WAL segments sequentially, which can fall behind under high write loads.
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 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
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.
Workload-Specific Database Design — This question tests Workload-Specific Database Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Migrate to Amazon Aurora with read replicas. — Option C is correct because Amazon Aurora's distributed storage architecture decouples compute from storage, allowing replicas to apply redo logs with minimal overhead compared to RDS for PostgreSQL's physical replication. Aurora's replicas share the same underlying storage volume, so replica lag is significantly reduced even under heavy write loads, while write performance on the primary remains unaffected due to the asynchronous, log-based replication mechanism.
What should I do if I get this DBS-C01 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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