DBS-C01 Workload-Specific Database Design Practice Question
An e-commerce platform uses Amazon DynamoDB for a shopping cart table with partition key 'user_id' and sort key 'product_id'. The table experiences throttled write requests during flash sales. The access pattern includes reading the entire cart at checkout. Which design change would improve write performance without changing the read pattern?
⚠ Common exam trap
It's easy for candidates to confuse DAX as a write accelerator or assume that simply increasing provisioned capacity is sufficient, overlooking that on-demand mode with adaptive capacity is the correct solution for unpredictable traffic spikes without schema changes.
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
✓
Enable DynamoDB Adaptive Capacity and ensure the table uses on-demand capacity mode
Enabling DynamoDB Adaptive Capacity with on-demand capacity mode automatically scales write capacity to handle traffic spikes during flash sales without requiring manual provisioning. This eliminates throttling while preserving the existing table schema (partition key 'user_id' and sort key 'product_id'), so the read pattern of querying the entire cart by user_id remains unchanged.
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 Accelerator (DAX) to cache writes
Why it's wrong here
DAX caches reads, not writes; writes still go to the table.
- ✗
Increase the provisioned write capacity units (WCU) to a higher value
Why it's wrong here
Increasing WCU does not resolve hot partition issues caused by a single user_id.
- ✗
Change the table design to use only partition key 'user_id' and remove the sort key
Why it's wrong here
Removing sort key would prevent storing multiple products per user, breaking the cart functionality.
- ✓
Enable DynamoDB Adaptive Capacity and ensure the table uses on-demand capacity mode
Why this is correct
Adaptive capacity helps distribute traffic across partitions, and on-demand mode handles spikes.
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