- A
Amazon DynamoDB with Global Secondary Indexes
Why wrong: DynamoDB is not optimized for real-time feed aggregation.
- B
Amazon S3 with Select and Glacier
Why wrong: S3 is object storage, not a real-time database.
- C
Amazon RDS for PostgreSQL with read replicas
Why wrong: RDS is not designed for real-time sub-millisecond updates.
- D
Amazon ElastiCache for Redis with sorted sets and pub/sub
Redis provides real-time data structures and pub/sub for feeds.
Question 1,525 of 1,730
DBS-C01 Workload-Specific Database Design Practice Question
This DBS-C01 practice question tests your understanding of workload-specific database design. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 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?
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.
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.
- ✗
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.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often 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.
Detailed technical explanation
How to think about this question
Redis sorted sets use a skip list and hash table internally to maintain order by score, allowing O(log N) operations for adding, updating, or querying items by rank—critical for ranking posts in a feed. The pub/sub feature uses channels and pattern matching to broadcast new posts to all subscribers instantly, with no persistence overhead, enabling sub-millisecond propagation. In a real-world scenario, a startup could use a sorted set per user to store post IDs with timestamps as scores, and pub/sub to notify active clients of new entries, achieving both personalization and real-time updates without database load.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
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 |
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this DBS-C01 question test?
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: 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.
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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Last reviewed: Jul 4, 2026
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