- A
Change the table's partition key to customer_id and use a composite sort key.
Why wrong: Changing the primary key requires creating a new table and migrating data, which is a major redesign.
- B
Create a Local Secondary Index (LSI) on customer_id.
Why wrong: An LSI must use the same partition key as the base table; since the base table uses transaction_id, an LSI cannot use customer_id as partition key.
- C
Create a Global Secondary Index (GSI) with customer_id as the partition key and timestamp as the sort key.
A GSI allows querying by customer_id and timestamp range without modifying the base table.
- D
Use the Scan operation with a filter expression for customer_id and timestamp.
Why wrong: Scan reads the entire table and is inefficient, especially for large tables.
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 financial services company uses Amazon DynamoDB to store transaction records. Each transaction has a unique transaction_id as the partition key and a timestamp as the sort key. The application frequently queries all transactions for a given customer within a date range. However, customer_id is not an attribute indexed for querying. The company wants to optimize these queries without redesigning the entire table schema. Which action should the company take?
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
Create a Global Secondary Index (GSI) with customer_id as the partition key and timestamp as the sort key.
Option C is correct because creating a Global Secondary Index (GSI) with customer_id as the partition key and timestamp as the sort key allows efficient querying of all transactions for a given customer within a date range without redesigning the base table. The GSI provides a new access pattern with its own partition and sort keys, enabling the Query operation on customer_id and timestamp, which is far more efficient than a Scan. This approach preserves the existing table schema and supports the required query pattern with minimal overhead.
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.
- ✗
Change the table's partition key to customer_id and use a composite sort key.
Why it's wrong here
Changing the primary key requires creating a new table and migrating data, which is a major redesign.
- ✗
Create a Local Secondary Index (LSI) on customer_id.
Why it's wrong here
An LSI must use the same partition key as the base table; since the base table uses transaction_id, an LSI cannot use customer_id as partition key.
- ✓
Create a Global Secondary Index (GSI) with customer_id as the partition key and timestamp as the sort key.
Why this is correct
A GSI allows querying by customer_id and timestamp range without modifying the base table.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use the Scan operation with a filter expression for customer_id and timestamp.
Why it's wrong here
Scan reads the entire table and is inefficient, especially for large tables.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse Local Secondary Indexes (LSIs) with Global Secondary Indexes (GSIs), assuming an LSI can be added later or can use a different partition key, when in fact LSIs must share the base table's partition key and can only be created at table creation time.
Detailed technical explanation
How to think about this question
A Global Secondary Index (GSI) in DynamoDB is a fully independent index with its own partition and sort keys, allowing queries on attributes not in the base table's primary key. The GSI is maintained asynchronously, meaning eventual consistency is the default, but strongly consistent reads are available at extra cost. In this scenario, the GSI on customer_id (partition key) and timestamp (sort key) enables the Query API to efficiently retrieve transactions for a customer within a date range using KeyConditionExpression, avoiding expensive full-table scans and supporting high-throughput workloads common in financial services.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
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: Create a Global Secondary Index (GSI) with customer_id as the partition key and timestamp as the sort key. — Option C is correct because creating a Global Secondary Index (GSI) with customer_id as the partition key and timestamp as the sort key allows efficient querying of all transactions for a given customer within a date range without redesigning the base table. The GSI provides a new access pattern with its own partition and sort keys, enabling the Query operation on customer_id and timestamp, which is far more efficient than a Scan. This approach preserves the existing table schema and supports the required query pattern with minimal overhead.
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: Jun 11, 2026
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