DBS-C01 Workload-Specific Database Design Practice Question
A company has a document database workload on Amazon DynamoDB that stores user session data. The application frequently updates session attributes (e.g., last activity timestamp). The current design stores the entire session as a single item and updates the entire item on each session activity. This is causing high write costs and throttling. Which design pattern would reduce write costs and improve performance?
⚠ Common exam trap
Candidates often confuse scaling solutions (increasing WCUs or adding DAX) with optimization patterns, failing to recognize that the real issue is the write amplification caused by full-item updates rather than insufficient capacity or read performance.
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
✓
Use UpdateItem with an update expression to modify only the changed attributes.
Using UpdateItem with an update expression allows you to modify only the specific attributes that changed (e.g., last activity timestamp) instead of rewriting the entire item. This reduces write consumption to a fraction of the original cost, since DynamoDB charges based on the size of the written data, and partial updates write only the changed attribute bytes. This directly addresses the high write costs and throttling caused by full-item overwrites.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Increase the write capacity units (WCUs) on the table.
Why it's wrong here
Increasing capacity increases cost and does not reduce the write unit consumption per update.
- ✓
Use UpdateItem with an update expression to modify only the changed attributes.
Why this is correct
Update expressions only write the changed attributes, consuming fewer write capacity units.
- ✗
Implement DynamoDB Accelerator (DAX) to cache the session data.
Why it's wrong here
DAX is a read cache and does not reduce write costs.
- ✗
Split the session item into multiple items, one per attribute.
Why it's wrong here
Splitting items complicates queries and may increase overall write cost due to multiple item updates.
Go deeper
Related to this question
About these practice questions
One of 1,663 original DBS-C01 practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DBS-C01 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 DBS-C01 exam.