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 healthcare company stores patient records in Amazon DynamoDB. Each record includes patient_id (partition key), visit_date (sort key), and a large JSON attribute for medical history. The application frequently queries recent visits for a patient and scans historical data for analytics. The scans on the medical history attribute cause high RCU consumption. The company wants to reduce costs and improve query performance. Which design should be implemented?
Compress the medical history attribute using gzip before storing in DynamoDB.
Why wrong: Compression reduces storage but not RCU consumption because DynamoDB reads the entire item.
B
Move the medical history attribute to a separate table with patient_id as partition key and visit_date as sort key. Use DynamoDB Streams to keep both tables in sync.
Separating the large attribute reduces RCU consumption for queries that do not need it.
C
Enable DynamoDB Accelerator (DAX) for the table to cache frequent queries.
Why wrong: DAX does not reduce the cost of scanning large attributes.
D
Use Amazon S3 to store the medical history as a separate object and reference it from DynamoDB.
Why wrong: This adds complexity and latency for accessing medical history.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Move the medical history attribute to a separate table with patient_id as partition key and visit_date as sort key. Use DynamoDB Streams to keep both tables in sync.
Option B is correct because it separates the large, infrequently accessed medical history attribute from the frequently queried core record, reducing the item size for common queries and thus lowering RCU consumption. By using DynamoDB Streams to synchronize the two tables, you maintain data consistency without adding complexity to the application, and queries against the main table become faster and cheaper since they no longer read the large JSON payload.
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.
✗
Compress the medical history attribute using gzip before storing in DynamoDB.
Why it's wrong here
Compression reduces storage but not RCU consumption because DynamoDB reads the entire item.
✓
Move the medical history attribute to a separate table with patient_id as partition key and visit_date as sort key. Use DynamoDB Streams to keep both tables in sync.
Why this is correct
Separating the large attribute reduces RCU consumption for queries that do not need it.
Related concept
Read the scenario before looking for a memorised answer.
✗
Enable DynamoDB Accelerator (DAX) for the table to cache frequent queries.
Why it's wrong here
DAX does not reduce the cost of scanning large attributes.
✗
Use Amazon S3 to store the medical history as a separate object and reference it from DynamoDB.
Why it's wrong here
This adds complexity and latency for accessing medical history.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often choose compression (Option A) thinking it reduces storage and read costs, but DynamoDB does not natively support compression and charges based on the actual stored item size, so compression must be handled at the application layer and does not reduce RCU consumption.
Detailed technical explanation
How to think about this question
DynamoDB charges RCUs based on item size rounded up to the nearest 4 KB for eventually consistent reads and 8 KB for strongly consistent reads. By moving the large medical history attribute to a separate table, the main table's items become much smaller (e.g., a few hundred bytes instead of tens of KB), drastically reducing RCU consumption per query. DynamoDB Streams captures item-level changes in near real-time, enabling you to replicate updates to the secondary table with minimal latency, and you can use AWS Lambda to process the stream and keep the tables in sync without custom polling logic.
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.
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: Move the medical history attribute to a separate table with patient_id as partition key and visit_date as sort key. Use DynamoDB Streams to keep both tables in sync. — Option B is correct because it separates the large, infrequently accessed medical history attribute from the frequently queried core record, reducing the item size for common queries and thus lowering RCU consumption. By using DynamoDB Streams to synchronize the two tables, you maintain data consistency without adding complexity to the application, and queries against the main table become faster and cheaper since they no longer read the large JSON payload.
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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Question Discussion
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