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 partition key of customer_id and a sort key of transaction_timestamp. The application queries transactions for a specific customer within a date range. Recently, the query latency increased significantly for customers with a large number of transactions. The company needs to improve query performance without changing the application code. The table is provisioned with 5000 RCUs and 2000 WCUs. Which design change should be made to optimize for this workload?
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 with customer_id as partition key and transaction_timestamp as sort key.
Option A is correct because creating a global secondary index (GSI) with customer_id as the partition key and transaction_timestamp as the sort key allows efficient querying of transactions for a specific customer within a date range. The existing table's sort key is transaction_timestamp, but the GSI provides a separate index optimized for this access pattern, avoiding full table scans on large customer partitions. This improves query performance without requiring application code changes, as the application can query the GSI directly.
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.
✓
Create a global secondary index with customer_id as partition key and transaction_timestamp as sort key.
Why this is correct
A GSI with the same key structure allows efficient querying without impacting the base table.
Related concept
Read the scenario before looking for a memorised answer.
✗
Enable DynamoDB Accelerator (DAX) on the table.
Why it's wrong here
DAX reduces read latency for cached data but does not address the underlying query pattern inefficiency.
✗
Increase the provisioned RCUs to 10000.
Why it's wrong here
Increasing RCUs may help throughput but does not improve query latency for large result sets.
✗
Change the sort key to a composite key including a tenant identifier.
Why it's wrong here
Changing the sort key would require application changes and data migration.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse caching (DAX) with query optimization, or assume that increasing RCUs alone will solve latency issues, when the real bottleneck is the inefficient scan of large partitions due to the lack of an appropriate index.
Detailed technical explanation
How to think about this question
Under the hood, DynamoDB partitions data by partition key; for a customer with many transactions, all items reside in the same partition, causing a query to scan all items before applying the sort key filter. A GSI with the same partition and sort key as the query pattern allows DynamoDB to directly seek the requested range of sort keys, reducing I/O and latency. In practice, this is a common anti-pattern where hot keys (customers with high transaction volumes) degrade performance, and a GSI provides a separate physical index that can be provisioned with its own read/write capacity.
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.
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 with customer_id as partition key and transaction_timestamp as sort key. — Option A is correct because creating a global secondary index (GSI) with customer_id as the partition key and transaction_timestamp as the sort key allows efficient querying of transactions for a specific customer within a date range. The existing table's sort key is transaction_timestamp, but the GSI provides a separate index optimized for this access pattern, avoiding full table scans on large customer partitions. This improves query performance without requiring application code changes, as the application can query the GSI directly.
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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Question Discussion
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