SOA-C02 Cost and Performance Optimization Practice Question
This SOA-C02 practice question tests your understanding of cost and performance optimization. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company uses an Amazon DynamoDB table with provisioned capacity. The average write usage is 500 write capacity units (WCU) but regularly spikes to 2,000 WCU during business hours. The SysOps administrator wants to reduce costs without affecting performance during the spikes. Which solution should the administrator implement?
Auto scaling adjusts provisioned capacity based on actual usage, handling spikes and reducing cost during low usage.
B
Switch to DynamoDB on-demand capacity mode
Why wrong: On-demand capacity is best for unpredictable workloads; for predictable spikes, auto scaling on provisioned capacity is more cost-effective.
C
Purchase reserved capacity for 2,000 WCU
Why wrong: Reserved capacity requires a commitment to a specific throughput, leading to waste if the average usage is lower.
D
Use DynamoDB Time to Live (TTL) to delete old items
Why wrong: TTL helps reduce storage costs but does not affect write capacity usage or cost optimization for throughput.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable DynamoDB auto scaling
DynamoDB auto scaling allows the table to automatically adjust its provisioned write capacity between a minimum and maximum range based on actual traffic. By setting the minimum WCU to cover the average usage (500) and the maximum to handle the spikes (2,000), the administrator pays only for the baseline capacity most of the time, while the service scales up during spikes without manual intervention or over-provisioning.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 auto scaling
Why this is correct
Auto scaling adjusts provisioned capacity based on actual usage, handling spikes and reducing cost during low usage.
Related concept
Read the scenario before looking for a memorised answer.
✗
Switch to DynamoDB on-demand capacity mode
Why it's wrong here
On-demand capacity is best for unpredictable workloads; for predictable spikes, auto scaling on provisioned capacity is more cost-effective.
✗
Purchase reserved capacity for 2,000 WCU
Why it's wrong here
Reserved capacity requires a commitment to a specific throughput, leading to waste if the average usage is lower.
✗
Use DynamoDB Time to Live (TTL) to delete old items
Why it's wrong here
TTL helps reduce storage costs but does not affect write capacity usage or cost optimization for throughput.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse on-demand mode as a cost-saving measure for spiky workloads, but in reality, on-demand is more expensive than provisioned capacity with auto scaling when there is a predictable baseline, and the question specifically asks to reduce costs without affecting performance.
Detailed technical explanation
How to think about this question
DynamoDB auto scaling uses the AWS Application Auto Scaling service, which monitors the consumed write capacity metric (ConsumedWriteCapacityUnits) via CloudWatch alarms and adjusts the provisioned WCU using a target tracking scaling policy (e.g., targeting 70% utilization). The scaling happens asynchronously, typically within a few minutes, so for very rapid spikes, it is recommended to set a higher maximum WCU or use burst capacity (which provides up to 300 seconds of unused capacity) to absorb sudden increases until auto scaling catches up.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Cost and Performance Optimization — This question tests Cost and Performance Optimization — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Enable DynamoDB auto scaling — DynamoDB auto scaling allows the table to automatically adjust its provisioned write capacity between a minimum and maximum range based on actual traffic. By setting the minimum WCU to cover the average usage (500) and the maximum to handle the spikes (2,000), the administrator pays only for the baseline capacity most of the time, while the service scales up during spikes without manual intervention or over-provisioning.
What should I do if I get this SOA-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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