The answer is implementing table partitioning and using S3 as an external table for old partitions. This approach is correct because it leverages PostgreSQL’s native range partitioning to separate hot, frequently accessed data from cold, rarely accessed data, then uses extensions like `postgres_fdw` or `pg_parquet` to mount old partitions as foreign tables stored directly in Amazon S3. This keeps your OLTP workload on RDS fast and unencumbered while shifting archival storage to S3’s low-cost tiers, drastically reducing RDS storage bills without schema redesign. On the AWS Certified Database Specialty DBS-C01 exam, this scenario tests your understanding of hybrid storage patterns that balance performance and cost—a common trap is choosing full database migration to Aurora or simply deleting old rows, both of which either increase cost or lose data. Remember the memory tip: “Partition hot, archive cold, FDW to S3—your OLTP stays bold.”
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 a critical OLTP workload on Amazon RDS for PostgreSQL. The database size is 2 TB and growing. To reduce storage costs, the company wants to archive old data that is rarely accessed. Which approach is most cost-effective and minimally impacts performance?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Implement table partitioning and use S3 as an external table for old partitions.
Option C is correct because it uses PostgreSQL table partitioning (e.g., range partitioning by date) combined with the `postgres_fdw` or `pg_parquet` extension to treat old partitions as foreign tables stored in Amazon S3. This keeps the hot data in RDS for fast OLTP access while offloading cold data to low-cost S3 storage, minimizing performance impact and reducing storage costs without requiring a full migration or schema redesign.
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.
✗
Move the database to Amazon Aurora PostgreSQL with storage auto-scaling.
Why it's wrong here
Aurora storage is not cheaper than RDS for cold data.
✗
Migrate the entire database to Amazon DynamoDB.
Why it's wrong here
Relational schema and joins would be difficult.
✓
Implement table partitioning and use S3 as an external table for old partitions.
Why this is correct
Reduces primary storage cost while preserving data access.
Related concept
Read the scenario before looking for a memorised answer.
✗
Delete old rows and run VACUUM FULL to reclaim space.
Why it's wrong here
VACUUM FULL locks tables and is disruptive.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume deleting rows and running VACUUM FULL (Option D) reduces storage costs, but RDS bills for allocated storage, not used space, so reclaiming space does not lower the bill and VACUUM FULL can cause significant performance disruption.
Detailed technical explanation
How to think about this question
PostgreSQL table partitioning (declarative partitioning introduced in PG 10) allows pruning queries to scan only relevant partitions, improving performance for OLTP workloads. Using `postgres_fdw` or `pg_parquet` with S3 as an external table enables transparent querying of archived partitions without moving data back into RDS, leveraging S3's lifecycle policies for further cost optimization (e.g., transition to S3 Glacier after 30 days). In practice, you can automate partition detachment and export to S3 using pg_cron or AWS Lambda, ensuring minimal impact on the primary database.
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 startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
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: Implement table partitioning and use S3 as an external table for old partitions. — Option C is correct because it uses PostgreSQL table partitioning (e.g., range partitioning by date) combined with the `postgres_fdw` or `pg_parquet` extension to treat old partitions as foreign tables stored in Amazon S3. This keeps the hot data in RDS for fast OLTP access while offloading cold data to low-cost S3 storage, minimizing performance impact and reducing storage costs without requiring a full migration or schema redesign.
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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