The correct choice is to create a Global Secondary Index on user_id because a Global Secondary Index (GSI) allows you to query by a non-key attribute like user_id efficiently without modifying the base table’s primary key structure. In DynamoDB, a GSI provides a separate index with its own partition key, enabling fast lookups on user_id with eventual consistency, avoiding a full table scan. On the AWS Certified Database Specialty DBS-C01 exam, this scenario tests your understanding of when to use secondary indexes versus redesigning the base key—a common trap is assuming you must change the primary key, which would break existing access patterns. Remember the memory tip: “GSI for extra queries, keep the base key clean.”
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 developer created a DynamoDB table 'UserSessions' with a simple primary key. The application needs to query by user_id as well. What design change should the developer make to support this query efficiently?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "primary"
Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a Global Secondary Index on user_id
Option D is correct because a Global Secondary Index (GSI) on user_id allows efficient querying by user_id without altering the base table's primary key structure. The base table uses a simple primary key (likely session_id), and a GSI provides a separate index with its own partition key (user_id) to support non-key attribute queries with eventual consistency, enabling the application to query by user_id efficiently without scanning the entire table.
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.
✗
Use a Scan operation with a filter
Why it's wrong here
Scan is inefficient for frequent queries.
✗
Add a sort key to the table
Why it's wrong here
Adding a sort key does not help query by user_id unless user_id is the partition key.
✗
Create a Local Secondary Index on user_id
Why it's wrong here
LSI requires the same partition key (session_id), so it cannot query by user_id alone.
✓
Create a Global Secondary Index on user_id
Why this is correct
A GSI enables efficient querying on user_id.
Clue confirmation
The clue word "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
AWS often tests the misconception that a Local Secondary Index can be used to query on any attribute, but the trap here is that an LSI requires the same partition key as the base table, so it cannot index user_id as a partition key unless user_id is already the base table's partition key.
Detailed technical explanation
How to think about this question
Under the hood, a GSI in DynamoDB maintains its own partition key and optional sort key, allowing queries on attributes not part of the base table's primary key. The GSI is replicated asynchronously from the base table, so queries are eventually consistent by default, but can be configured for strong consistency if needed. In real-world scenarios, such as a user session table where the primary key is session_id, a GSI on user_id enables efficient lookups for all sessions belonging to a specific user, which is critical for user-facing applications that need to retrieve session history without full table scans.
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: Create a Global Secondary Index on user_id — Option D is correct because a Global Secondary Index (GSI) on user_id allows efficient querying by user_id without altering the base table's primary key structure. The base table uses a simple primary key (likely session_id), and a GSI provides a separate index with its own partition key (user_id) to support non-key attribute queries with eventual consistency, enabling the application to query by user_id efficiently without scanning the entire table.
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: "primary". Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
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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