SAA-C03 Design Cost-Optimized Architectures Practice Question
A batch analytics job has unpredictable DynamoDB traffic with long idle periods and occasional spikes. Which capacity mode should minimize operational overhead and avoid paying for idle provisioned capacity? The design must avoid adding custom operational scripts.
⚠ Common exam trap
A common mix-up: candidates confuse 'reserved capacity' (a pricing discount for provisioned capacity) with a capacity mode, or assume that provisioned capacity set for peak traffic is cost-effective, ignoring the cost of idle periods.
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
✓
DynamoDB on-demand capacity mode
DynamoDB on-demand capacity mode automatically scales to handle unpredictable traffic spikes and idle periods without requiring any capacity planning or management. It charges only for the reads and writes you perform, eliminating the cost of idle provisioned capacity and avoiding the need for custom scripts to adjust capacity.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
DynamoDB on-demand capacity mode
Why this is correct
On-demand capacity mode enables DynamoDB to automatically scale to match your workload's actual traffic, charging per read and write request (pay-per-request) rather than for provisioned capacity. For a batch analytics job with unpredictable traffic, this eliminates manual capacity planning, avoids throttling during sudden spikes, and ensures you only pay for the requests actually processed, making it the most cost-effective and operationally simple choice.
- ✗
Reserved capacity for maximum daily traffic
Why it's wrong here
Reserved capacity is a discounted billing commitment for a fixed amount of capacity over a 1- or 3-year term, designed for stable, predictable workloads. If you reserve enough to cover your maximum daily traffic, you pay for that capacity continuously even when the batch job is idle or traffic is far below the peak, resulting in significant waste and no flexibility to adapt to unpredictable demand.
- ✗
Provisioned capacity set for peak traffic
Why it's wrong here
Provisioned capacity mode requires you to specify a fixed number of read and write capacity units, and you pay for that configured capacity even when it is unused. Setting it to peak traffic ensures you rarely experience throttling, but you are paying for peak capacity 24/7, and while DynamoDB Auto Scaling can adjust capacity, it reacts after usage changes and cannot handle abrupt bursty traffic preceding a scale-out action, leaving you either throttled or overpaying.
- ✗
Global tables in every Region
Why it's wrong here
Global tables replicate your DynamoDB data across multiple AWS Regions using multi-Region write forwarding, which adds cross-region replication latency and incurs additional write costs for every update. They are intended for disaster recovery or low-latency global access, but they do not affect capacity mode or cost per request in any region, so they would neither absorb idle capacity waste nor address the unpredictability of traffic in a single-region batch job.
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