DEA-C01 Data Store Management Practice Question
A company needs to store relational data that requires complex joins and transactional consistency. The workload is predictable and the data size is less than 500 GB. Which AWS service is MOST cost-effective for this use case?
⚠ Common exam trap
A common mix-up: candidates choose Amazon Redshift for any data that involves joins or analytics, ignoring that it is cost-prohibitive and architecturally mismatched for transactional, sub-500 GB workloads, while RDS is the correct relational database service for this scale.
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
✓
Amazon RDS for PostgreSQL
Amazon RDS for PostgreSQL is the most cost-effective choice because it provides a fully managed relational database service that supports complex joins and transactional consistency (ACID compliance) for predictable workloads under 500 GB. Unlike Redshift, which is optimized for petabyte-scale analytics, RDS offers lower cost for this data size and workload pattern, while DynamoDB lacks native SQL join capabilities and S3 is not a relational database.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Amazon Redshift
Why it's wrong here
Amazon Redshift is a columnar data warehouse tuned for large-scale analytical aggregation, and its cluster provisioning costs exceed what a sub-500 GB transactional workload justifies. It is tempting because it handles SQL joins, but would be correct for petabyte-scale OLAP reporting, not predictable OLTP with transactional consistency.
- ✗
Amazon S3
Why it's wrong here
Amazon S3 is object storage with no relational engine, so it cannot perform joins or enforce transactional consistency. It is tempting because it is inexpensive for sub-500 GB datasets, and would be correct for storing files, backups or data lake objects rather than a transactional relational database.
- ✓
Amazon RDS for PostgreSQL
Why this is correct
Amazon RDS for PostgreSQL provides full relational joins and ACID transactional consistency, which the workload demands. For predictable traffic under 500 GB, a single provisioned instance avoids the cost of distributed engines such as Aurora or DynamoDB, making it most cost-effective.
- ✗
Amazon DynamoDB
Why it's wrong here
DynamoDB is NoSQL and does not support complex joins or transactions across multiple tables.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
Go deeper
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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