DBS-C01 Workload-Specific Database Design Practice Question
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?
⚠ Common exam trap
Test-takers frequently 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.
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.
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.
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.
- ✗
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DBS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DBS-C01 exam.