DBS-C01 Workload-Specific Database Design Practice Question
A company is designing a new e-commerce platform using Amazon DynamoDB. The workload requires single-digit millisecond latency for user session data, which is accessed by session token. The session data is temporary and should be automatically deleted after 24 hours. Which DynamoDB design should the database specialist recommend?
⚠ Common exam trap
Many candidates confuse DynamoDB TTL with a feature that provides real-time or immediate deletion, when in fact TTL deletes items asynchronously in the background, typically within a few minutes to 48 hours, which is acceptable for temporary session data but not for compliance-driven immediate removal.
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 Time to Live (TTL) on the session token attribute
DynamoDB Time to Live (TTL) automatically deletes expired items after a specified timestamp, making it ideal for session data that must be removed after 24 hours. This approach requires no additional infrastructure, meets the single-digit millisecond latency requirement by using the session token as the primary key, and ensures automatic cleanup without manual intervention or added cost.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Create an AWS Lambda function that runs every hour and deletes expired session data
Why it's wrong here
Lambda-based deletion is possible but add complexity and potential cost, and is not the simplest design.
- ✗
Store session data in Amazon S3 with a lifecycle policy to delete objects after 24 hours
Why it's wrong here
S3 can handle session data but does not provide the required single-digit millisecond latency for session token lookups.
- ✗
Use DynamoDB Accelerator (DAX) to cache session data and set a 24-hour TTL on the cache
Why it's wrong here
DAX is an in-memory cache that can improve latency but does not automatically delete items from the DynamoDB table.
- ✓
Enable DynamoDB Time to Live (TTL) on the session token attribute
Why this is correct
TTL automatically deletes items after a specified expiry timestamp, meeting the 24-hour deletion requirement.
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