DEA-C01 Data Store Management Practice Question
A data engineer needs to store semi-structured JSON data from IoT devices. The data is written frequently and read occasionally. Which AWS service is MOST cost-effective for this use case?
⚠ Common exam trap
Many exam-takers choose Amazon ElastiCache for Redis due to its speed and JSON module support, but they overlook that it is not designed for durable, cost-effective long-term storage of semi-structured data, and DynamoDB's native JSON support and pay-per-request pricing make it the more economical choice for this specific write-frequent, read-occasional pattern.
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 DynamoDB
Amazon DynamoDB is the most cost-effective choice because it is a fully managed NoSQL key-value and document database that natively supports semi-structured JSON data, offers single-digit millisecond latency for frequent writes, and provides a pay-per-request pricing model ideal for workloads with occasional reads. Its on-demand capacity mode automatically scales to handle high write throughput without provisioning, making it cheaper than provisioned alternatives for spiky or unpredictable IoT ingestion patterns.
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 ElastiCache for Redis
Why it's wrong here
ElastiCache for Redis is an in-memory cache, so storing frequent IoT JSON writes there incurs memory-resident pricing and risks data loss on eviction or restart. It is tempting for high-throughput ingestion, but it suits caching or session data, whereas durable, infrequent-read semi-structured storage points to Amazon S3.
- ✓
Amazon DynamoDB
Why this is correct
DynamoDB is a serverless key-value store billed per request, so frequent writes and occasional reads incur no idle capacity cost, unlike always-on provisioned databases. It natively stores JSON documents, satisfying the semi-structured IoT payload requirement at the lowest cost.
- ✗
Amazon RDS for MySQL
Why it's wrong here
RDS for MySQL stores JSON in row-based tables on provisioned instances, so continuous IoT writes pay for idle database capacity regardless of read volume. It fits transactional relational workloads needing joins and ACID guarantees, not cheap semi-structured object storage.
- ✗
Amazon Redshift
Why it's wrong here
Redshift is a columnar data warehouse requiring provisioned clusters or serverless compute, so frequent small IoT JSON writes incur cost and latency without benefiting occasional reads. It suits analytical SQL over structured, aggregated data at scale, not raw semi-structured ingestion.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DEA-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DEA-C01 exam.