DEA-C01 Data Store Management Practice Question
A data engineer is designing a data store for a real-time leaderboard application that requires sub-millisecond read and write latency. The leaderboard stores scores for millions of users and needs to be sorted by score. Which AWS service should the engineer use?
⚠ Common exam trap
Many exam-takers choose DynamoDB (Option B) because it is a common NoSQL choice for high-performance applications, but they overlook that DynamoDB lacks a native sorted data structure and requires costly scan operations to retrieve a globally sorted leaderboard, whereas Redis sorted sets are purpose-built for this exact use case.
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 a sorted set
Amazon ElastiCache for Redis provides a sorted set data structure (ZADD/ZRANGE commands) that maintains elements ordered by a numeric score with O(log N) complexity for both writes and reads, enabling sub-millisecond latency for real-time leaderboard updates and queries. This is the only option purpose-built for in-memory, sorted, real-time leaderboards at scale.
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 RDS for PostgreSQL with an index on score
Why it's wrong here
Amazon RDS for PostgreSQL, even with an index on score, would struggle to consistently achieve sub-millisecond read and write latency for millions of users due to the inherent overhead of a relational database managing ACID transactions and disk I/O at that scale. While an index assists with sorting, it doesn't overcome the fundamental latency limitations for real-time leaderboards. RDS is a robust choice for transactional applications requiring strong consistency and complex querying, where latencies in the single-digit milliseconds are acceptable.
- ✗
Amazon DynamoDB with a global secondary index on score
Why it's wrong here
DynamoDB can't natively maintain a sorted set with sub-millisecond updates.
- ✓
Amazon ElastiCache for Redis with a sorted set
Why this is correct
Redis sorted sets provide O(log N) operations and sub-millisecond latency.
- ✗
Amazon Neptune with a graph model
Why it's wrong here
Neptune is for graph data, not leaderboards.
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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.