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.
Network Topology
Refer to the exhibit. A company uses this DynamoDB table to store user session data. The application frequently queries by user_id alone to get all sessions for a user. However, the query is slow. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The table's partition key is session_id, not user_id, so querying by user_id requires a scan.
The table's primary key is session_id, not user_id. Querying by user_id without a secondary index forces DynamoDB to perform a full table scan, which reads every item and is significantly slower than a query operation. This is the most likely cause of the slow performance.
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.
✓
The table's partition key is session_id, not user_id, so querying by user_id requires a scan.
Why this is correct
Without a GSI on user_id, queries on user_id are scans.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The table has no sort key on user_id.
Why it's wrong here
user_id is a sort key, but it is only efficient when combined with session_id.
✗
The table has too many items, causing slow scans.
Why it's wrong here
10,000 items is not large; the issue is key design.
✗
The provisioned read capacity is too low.
Why it's wrong here
5 RCUs for 10,000 items is sufficient for small queries.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume any attribute can be queried efficiently, failing to recognize that DynamoDB requires a primary key or index for efficient lookups, and that a scan is the fallback for non-key attributes.
Detailed technical explanation
How to think about this question
DynamoDB queries are efficient only when using the table's primary key (partition key + optional sort key) or a secondary index. A scan operation reads every item in the table, consuming read capacity for all items regardless of whether they match the filter. For session data, a global secondary index on user_id would allow efficient queries without scanning, as DynamoDB would route directly to the relevant partition.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
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: The table's partition key is session_id, not user_id, so querying by user_id requires a scan. — The table's primary key is session_id, not user_id. Querying by user_id without a secondary index forces DynamoDB to perform a full table scan, which reads every item and is significantly slower than a query operation. This is the most likely cause of the slow performance.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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