DBS-C01 Workload-Specific Database Design Practice Question
A gaming company uses Amazon ElastiCache for Redis as a leaderboard for real-time game scores. The leaderboard is updated frequently by millions of users. The application uses sorted sets with player scores. Recently, the leaderboard update latency increased and the cache evictions spiked. The company needs to ensure low-latency updates and high availability. The current setup is a single Redis node. Which design should be implemented?
⚠ Common exam trap
Many candidates assume Multi-AZ (Option D) alone solves high availability and performance, but without sharding (cluster mode enabled), a single node remains a bottleneck for write-heavy workloads, and evictions will continue.
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
✓
Use a Redis Cluster with multiple shards. Enable AOF persistence and use a read replica for the leaderboard queries.
Redis Cluster with multiple shards distributes the write load across shards, reducing per-node pressure and evictions. Enabling AOF persistence ensures durability, while using a read replica for leaderboard queries offloads read traffic from the primary shard, maintaining low-latency updates. This design provides both horizontal scaling and high availability, addressing the increased update latency and eviction spikes.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Upgrade to a larger single Redis node instance type to handle the load.
Why it's wrong here
Scaling vertically may temporarily help but does not address the need for high availability and sharding.
- ✗
Replace Redis with DynamoDB for the leaderboard, using a global secondary index on score.
Why it's wrong here
DynamoDB is not optimized for real-time leaderboard operations like sorted sets.
- ✓
Use a Redis Cluster with multiple shards. Enable AOF persistence and use a read replica for the leaderboard queries.
Why this is correct
Redis Cluster distributes data across shards, reducing load per node. Read replicas can handle queries, and AOF ensures durability.
- ✗
Use ElastiCache for Redis with cluster mode disabled and enable Multi-AZ.
Why it's wrong here
Cluster mode disabled means single node, Multi-AZ provides failover but not sharding.
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