SAA-C03 Design High-Performing Architectures Practice Question
A company is using Amazon DynamoDB to store real-time session data. The application requires response times in the sub-millisecond range for frequently accessed keys. The current DynamoDB latency is around 10-15 milliseconds. What should the architect implement to meet the performance goal?
⚠ Common exam trap
SAA-C03 often tests the misconception that adding read capacity (RCUs) or replicating data geographically reduces latency — both address throughput or availability, not the sub-millisecond read latency that only an in-memory cache like DAX can deliver.
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
✓
Implement Amazon DynamoDB Accelerator (DAX).
DynamoDB Accelerator (DAX) is an in-memory cache purpose-built for DynamoDB that delivers microsecond response times for eventually consistent reads — well within the sub-millisecond requirement. DAX sits in front of the table as a write-through cache, so frequently accessed keys are served from RAM rather than from DynamoDB's SSD-backed storage, eliminating the 10-15 ms round trip. It requires only a minor application change (swap the DynamoDB client for the DAX client) and is the standard AWS answer for 'sub-millisecond DynamoDB reads.'
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Enable DynamoDB Streams and use Lambda to update ElastiCache.
Why it's wrong here
While this approach can work for caching, it involves significant architectural complexity and development effort. The application would need to manage cache invalidation and consistency manually, whereas DAX provides a seamless, API-compatible caching layer that requires no code changes.
- ✗
Increase the Provisioned Read Capacity Units (RCUs) for the table.
Why it's wrong here
Increasing RCUs allows for a higher volume of requests but does not inherently reduce the latency of an individual request. DynamoDB's native latency is typically in the single-digit to low-double-digit millisecond range, which is still slower than the microsecond latency provided by DAX.
- ✓
Implement Amazon DynamoDB Accelerator (DAX).
Why this is correct
DAX is specifically designed to provide microsecond response times for DynamoDB reads. It handles the cache management and is API-compatible, meaning the application can use existing DynamoDB SDKs to access the cache, making it the most efficient way to achieve sub-millisecond latency.
- ✗
Use Global Tables to replicate data closer to the application nodes.
Why it's wrong here
Global Tables reduce latency for users in different geographic regions by providing local endpoints. However, if the application and the database are already in the same region, Global Tables will not reduce the base latency of DynamoDB below its standard millisecond range.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Amazon Web Services exam blueprint
This SAA-C03 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 SAA-C03 exam.