- A
Switch to larger DynamoDB instance types to handle larger items.
Why wrong: DynamoDB is serverless; there are no instance types.
- B
Use DynamoDB Accelerator (DAX) to cache the cart data.
Why wrong: DAX improves read performance but does not reduce read costs; it adds additional cost.
- C
Compress the cart items before storing them in DynamoDB and decompress on read.
Compression reduces the item size, lowering RCU consumption and cost.
- D
Normalize the cart data into separate tables for cart headers and line items.
Why wrong: Normalization increases the number of read operations, increasing costs.
Question 1,371 of 1,730
DBS-C01 Workload-Specific Database Design Practice Question
This DBS-C01 practice question tests your understanding of workload-specific database design. 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 retail company uses Amazon DynamoDB to store shopping cart data. The cart items are frequently updated as users add or remove products. The application reads the entire cart each time the user views it. The cart size averages 50 KB but can reach up to 400 KB. The company wants to reduce read costs and improve performance. Which design change would be most effective?
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
✓
Compress the cart items before storing them in DynamoDB and decompress on read.
Option C is correct because compressing cart items before storing them in DynamoDB reduces the item size, which directly lowers read capacity unit (RCU) consumption since DynamoDB charges based on read item size rounded up to 4 KB increments. For a 400 KB item, compression can shrink it significantly, reducing the number of 4 KB blocks read and thus cutting costs. Decompression on read adds minimal CPU overhead but yields substantial performance gains by reducing network transfer time and read latency.
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.
- ✗
Switch to larger DynamoDB instance types to handle larger items.
Why it's wrong here
DynamoDB is serverless; there are no instance types.
- ✗
Use DynamoDB Accelerator (DAX) to cache the cart data.
Why it's wrong here
DAX improves read performance but does not reduce read costs; it adds additional cost.
- ✓
Compress the cart items before storing them in DynamoDB and decompress on read.
Why this is correct
Compression reduces the item size, lowering RCU consumption and cost.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Normalize the cart data into separate tables for cart headers and line items.
Why it's wrong here
Normalization increases the number of read operations, increasing costs.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume caching (DAX) is the universal performance fix, but the question specifically targets reducing read costs, not just latency, and DAX does not eliminate the underlying cost of reading large items from DynamoDB.
Detailed technical explanation
How to think about this question
DynamoDB read capacity units are calculated based on item size rounded up to the nearest 4 KB for eventually consistent reads and 4 KB for strongly consistent reads (double the cost). Compressing a 400 KB cart item by 50% reduces it to 200 KB, which consumes 50 RCUs (200/4) instead of 100 RCUs (400/4) for an eventually consistent read. This technique is especially effective for write-heavy workloads with large items, as compression reduces storage costs and write capacity units (WCUs) as well, since WCUs are based on 1 KB increments.
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.
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FAQ
Questions learners often ask
What does this DBS-C01 question test?
Workload-Specific Database Design — This question tests Workload-Specific Database Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Compress the cart items before storing them in DynamoDB and decompress on read. — Option C is correct because compressing cart items before storing them in DynamoDB reduces the item size, which directly lowers read capacity unit (RCU) consumption since DynamoDB charges based on read item size rounded up to 4 KB increments. For a 400 KB item, compression can shrink it significantly, reducing the number of 4 KB blocks read and thus cutting costs. Decompression on read adds minimal CPU overhead but yields substantial performance gains by reducing network transfer time and read latency.
What should I do if I get this DBS-C01 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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Last reviewed: Jul 4, 2026
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