DBS-C01 Workload-Specific Database Design Practice Question
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?
⚠ Common exam trap
Many candidates 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.
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 with customer_id as partition key and transaction_timestamp as sort key.
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.
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.
- ✗
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.
Go deeper
Related to this question
About these practice questions
This DBS-C01 question is part of Courseiva's 1,663-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
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.