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.
Which THREE factors should be considered when choosing between Amazon RDS and Amazon DynamoDB for a new application? (Choose 3.)
Cost of storage
Why wrong: Both have cost-effective options.
Need for encryption at rest
Why wrong: Both support encryption at rest.
Access patterns (predictable vs. ad-hoc)
DynamoDB suits predictable patterns; RDS for complex queries.
Scalability requirements (horizontal vs. vertical)
DynamoDB scales horizontally; RDS scales vertically.
Query complexity (joins, aggregations)
RDS supports complex queries; DynamoDB is simple key-value.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Access patterns (predictable vs. ad-hoc)
Amazon RDS is a relational database service that excels at complex queries involving joins and aggregations, while DynamoDB is a NoSQL key-value and document database optimized for predictable, high-scale access patterns. The choice between them hinges on whether the application requires relational features (RDS) or can tolerate denormalized schemas for low-latency, horizontal scaling (DynamoDB). Option C is correct because DynamoDB is designed for ad-hoc, single-key lookups and simple queries, whereas RDS supports complex, ad-hoc SQL queries with joins.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Cost of storage
Why it's wrong here
Both have cost-effective options.
Need for encryption at rest
Why it's wrong here
Both support encryption at rest.
Access patterns (predictable vs. ad-hoc)
Why this is correct
DynamoDB suits predictable patterns; RDS for complex queries.
Related concept
Read the scenario before looking for a memorised answer.
Scalability requirements (horizontal vs. vertical)
Why this is correct
DynamoDB scales horizontally; RDS scales vertically.
Related concept
Read the scenario before looking for a memorised answer.
Query complexity (joins, aggregations)
Why this is correct
RDS supports complex queries; DynamoDB is simple key-value.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates often assume encryption at rest is exclusive to one service, but both RDS and DynamoDB support it via AWS KMS, making it a non-differentiating factor.
Detailed technical explanation
DynamoDB uses a distributed hash table architecture that partitions data across multiple nodes, enabling horizontal scaling by adding more partitions, but it lacks native support for SQL joins or complex aggregations, requiring application-level handling. RDS, by contrast, runs a traditional relational engine (e.g., MySQL, PostgreSQL) that supports ACID transactions and complex query optimization, but scales vertically (larger instances) or via read replicas, not horizontally across shards. In a real-world scenario, an e-commerce application needing real-time inventory lookups (predictable access) would favor DynamoDB, while a financial reporting system requiring multi-table joins would require RDS.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
Workload-Specific Database Design — This question tests Workload-Specific Database Design — Read the scenario before looking for a memorised answer..
The correct answer is: Access patterns (predictable vs. ad-hoc) — Amazon RDS is a relational database service that excels at complex queries involving joins and aggregations, while DynamoDB is a NoSQL key-value and document database optimized for predictable, high-scale access patterns. The choice between them hinges on whether the application requires relational features (RDS) or can tolerate denormalized schemas for low-latency, horizontal scaling (DynamoDB). Option C is correct because DynamoDB is designed for ad-hoc, single-key lookups and simple queries, whereas RDS supports complex, ad-hoc SQL queries with joins.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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