Which Caching Layer Fixes Slow RDS Metadata Reads for a Mobile Game?

SAA-C03 By islever Editorial Last updated

Determine high-performing database solutions.

Short answer

C Add an Amazon ElastiCache for Redis layer in front of the database to serve metadata with sub-millisecond reads plus Redis replication and snapshots.

Question

A company has a mobile game that reads most of its metadata from an Amazon RDS DB instance. As the game increased in popularity, developers noticed slowdowns related to the game's metadata load times. Performance metrics indicate that simply scaling the database will not help. A solutions architect must explore all options that include capabilities for snapshots, replication, and sub-millisecond response times. What should the solutions architect recommend to solve these issues?
  1. Migrate the database to Amazon Aurora with Aurora Replicas.
  2. Migrate the database to Amazon DynamoDB with global tables.
  3. Add an Amazon ElastiCache for Redis layer in front of the database. Correct Answer
  4. Add an Amazon ElastiCache for Memcached layer in front of the database.

Key Takeaways

This question tests whether you match a cache-engine choice to explicit capability requirements — snapshots, replication, and sub-millisecond reads — where Memcached lacks persistence and replication and therefore cannot satisfy the stated criteria.

A mobile game whose metadata reads from Amazon RDS struggles with load times, and metrics show that scaling the database alone will not fix it. The solution must provide snapshots, replication, and sub-millisecond response times, which points to Amazon ElastiCache for Redis in front of the database (C) rather than Memcached, Aurora replicas, or DynamoDB.

Common mistake: Many candidates pick ElastiCache for Memcached (D) because it is also a sub-millisecond, multi-threaded cache, missing that Memcached offers no replication, no snapshots, and no persistence; others pick DynamoDB (B) for its sub-millisecond latency while ignoring the relational migration cost and the fact that RDS metadata caching, not replacement, is required.

Expert Analysis

Why the Answer Is Correct

The scenario is a classic read-heavy metadata access pattern: the game repeatedly reads mostly static metadata, and performance metrics explicitly state that scaling the RDS database will not help. Adding an Amazon ElastiCache for Redis layer in front of the database (C) absorbs those repeated reads in memory and removes the load from the DB instance entirely. Redis is the only in-memory option listed that meets every stated capability: sub-millisecond response times, replication (Redis replication groups with read replicas), and snapshots (backup and restore of the Redis cluster). Because the metadata is read-mostly, a cache-aside layer in front of RDS is the lowest-risk, highest-impact fix compared with re-platforming the database.

Why the Other Options Are Wrong

Aurora with Aurora Replicas (A) improves read scalability, but the metrics already indicate that scaling the database is not the answer, and it provides no caching tier to deliver the repeated metadata reads in microseconds. DynamoDB with global tables (B) does deliver single-digit millisecond latency and multi-Region replication, but it forces a full re-platforming of the metadata model from relational RDS and introduces a far larger migration risk than the problem requires. ElastiCache for Memcached (D) is a fast, horizontally scalable cache, yet it deliberately lacks replication, snapshots, and durability, so it fails the explicit capability list in the question even though it would help raw latency.

Community Comment Notes

Andy_09 captured the deciding logic plainly, noting that "Option C is better as we need replication and snapshots". LeonSauveterre reasoned through the same path, observing that option A would only help if the root cause were purely relational read-heavy traffic, but the metrics say scaling will not help, and that the DynamoDB migration is a substantial effort. JA2018 argued for B on DynamoDB's sub-millisecond latency and automatic scaling, which is a genuine strength but overlooks the cache-in-front-of-RDS intent. oskm linked AWS's own Redis vs Memcached comparison, and f07ed8f pointed out that the snapshots, replication, and sub-millisecond capabilities describe the caching layer being selected.

Official Reference

These links open the official vendor documentation in a new tab.

Exam Strategy

When a stem lists three or more concrete capabilities, treat each one as a filter: sub-millisecond latency plus replication plus snapshots is Redis, while Memcached answers only the latency filter. Ask yourself whether the question wants a new database or a layer in front of the existing one — "in front of" usually signals caching.

Frequently Asked Questions

Why is ElastiCache for Redis chosen over ElastiCache for Memcached here?

Redis supports replication, snapshots and persistence, while Memcached is a pure volatile cache with neither. The question explicitly requires replication and snapshots, so Redis is the only cache option that qualifies.

Why not migrate the RDS metadata to DynamoDB with global tables?

DynamoDB meets the sub-millisecond and replication goals, but it requires re-platforming the relational metadata model and global tables solve multi-Region writes, which this workload does not need. Caching in front of the existing RDS database is faster to deliver and lower risk.

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Community Votes

C
78%
B
22%

78% of anonymous learners picked answer C. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 9 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 9

  1. Andy_09 👍 20
    Option C is better as we need replication and snapshots
  2. JA2018 👍 2 Answered B
    Why I choose B? # 1 High-performance, low latency: DynamoDB is a NoSQL database designed for fast, sub-millisecond response times, which is crucial for handling the high volume of metadata requests from a popular mobile game. # 2 Scalability: DynamoDB scales automatically to handle fluctuating traffic without the need to manually manage database instances, making it ideal for a rapidly growing game. # 3 Global tables: This feature allows for geographically distributed data access, ensuring quick response times for players across different regions.
  3. f07ed8f 👍 2
    Thinking the capabilities with "snapshots, replication, and sub-millisecond response times" is for the Database or selected solution(ElastiCache).
  4. LeonSauveterre 👍 1 Answered C
    A - If the root cause is database-related (for example, read-heavy traffic), then OK. However, "Performance metrics indicate that simply scaling the database will not help." means that maybe caching is a more effective option. B - Migrating from a relational database to DynamoDB requires so much effort. Such a headache. C - ElastiCache for Redis supports replication and snapshots, and of course, sub-millisecond response times. D - Memcached lacks built-in persistence, which is why game applications rarely use it.
  5. osmk 👍 1 Answered C
    :https://aws.amazon.com/elasticache/redis-vs-memcached/
Show 4 more comments
  1. tch 👍 1 Answered C
    capabilities for snapshots, replication
  2. JunsK1e 👍 1 Answered C
    C is correct
  3. nbellaiche 👍 1 Answered C
    Réponse C
  4. Andy_09 👍 1
    Option D

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