DBS-C01 Workload-Specific Database Design Practice Question
A startup is building a social media application with a news feed feature. The feed must be personalized and updated in real-time as users post. Which AWS database service is best suited for this workload?
⚠ Common exam trap
Test-takers frequently choose DynamoDB or RDS because they are familiar with them for data storage, but they overlook the need for real-time, in-memory operations and the specific data structures (sorted sets, pub/sub) that only ElastiCache for Redis provides for this workload.
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 ElastiCache for Redis with sorted sets and pub/sub
Amazon ElastiCache for Redis is the best choice because it provides in-memory data structures like sorted sets for ranking and scoring personalized feeds, and pub/sub for real-time notifications when new posts are published. This combination enables low-latency, real-time feed updates without the overhead of disk-based storage, making it ideal for a social media news feed that must be both personalized and updated in real-time.
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 DynamoDB with Global Secondary Indexes
Why it's wrong here
DynamoDB is not optimized for real-time feed aggregation.
- ✗
Amazon S3 with Select and Glacier
Why it's wrong here
S3 is object storage, not a real-time database.
- ✗
Amazon RDS for PostgreSQL with read replicas
Why it's wrong here
RDS is not designed for real-time sub-millisecond updates.
- ✓
Amazon ElastiCache for Redis with sorted sets and pub/sub
Why this is correct
Redis provides real-time data structures and pub/sub for feeds.
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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