The correct design change is to create a Global Secondary Index on CustomerID. This is because a Global Secondary Index (GSI) allows you to query on non-key attributes efficiently by providing an alternative partition and sort key structure, bypassing the need for a costly full table scan. In DynamoDB, without a GSI, a query on a non-key attribute like CustomerID would force a Scan operation, which degrades performance as the table grows. On the AWS Certified Database Specialty DBS-C01 exam, this scenario tests your understanding of when to use GSIs versus Local Secondary Indexes (LSIs) or table redesigns—a common trap is choosing an LSI, which cannot use a different partition key. Remember the memory tip: “GSI for any key, LSI for the same key”—GSIs give you flexibility to index any attribute as a new partition key, making them ideal for optimizing queries on non-key attributes like CustomerID.
DBS-C01 Workload-Specific Database Design Practice Question
This DBS-C01 practice question tests your understanding of workload-specific database design. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
An e-commerce application uses Amazon DynamoDB as its primary database. The table stores order data with a partition key of 'OrderID' and a sort key of 'OrderDate'. The application frequently queries orders by customer ID (which is not a key attribute). What design change would improve query performance?
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 CustomerID
Option C is correct because creating a Global Secondary Index (GSI) on CustomerID allows efficient querying by that attribute without scanning the entire table. A GSI has its own partition and sort keys, enabling fast lookups on non-key attributes. This directly addresses the performance issue of frequent queries by CustomerID, which otherwise would require a full table scan.
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.
✗
Enable DynamoDB Streams and export to Amazon Elasticsearch Service
Why it's wrong here
This adds complexity and latency; not optimal for simple query improvement.
✗
Use DynamoDB Accelerator (DAX) to cache queries
Why it's wrong here
DAX caches results but does not help with querying by non-key attributes.
✓
Create a Global Secondary Index on CustomerID
Why this is correct
GSI allows querying by CustomerID efficiently.
Clue confirmation
The clue word "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Create a Local Secondary Index on CustomerID
Why it's wrong here
LSI requires same partition key; OrderID is the partition key, so LSI on CustomerID is not possible without changing table structure.
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 used to query by a non-key attribute without the partition key, but LSIs require the same partition key as the base table and cannot be added after table creation.
Detailed technical explanation
How to think about this question
A Global Secondary Index (GSI) in DynamoDB is essentially a separate table that is automatically maintained and can have a different partition key and sort key from the base table. When you query a GSI, you pay for read capacity units based on the index's provisioned throughput, and the index can be created or deleted at any time. In contrast, a Local Secondary Index (LSI) shares the base table's partition key and can only be defined during table creation, making it inflexible for new access patterns like querying by CustomerID alone.
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 CustomerID — Option C is correct because creating a Global Secondary Index (GSI) on CustomerID allows efficient querying by that attribute without scanning the entire table. A GSI has its own partition and sort keys, enabling fast lookups on non-key attributes. This directly addresses the performance issue of frequent queries by CustomerID, which otherwise would require a full table scan.
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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