DBS-C01 Workload-Specific Database Design Practice Question
A company uses Amazon DynamoDB to store order data. The table has a primary key (OrderID) and a Global Secondary Index (GSI) on CustomerID. The application often queries for all orders of a customer sorted by order date. The GSI projects only the keys. The queries are slow. What should the team do to improve query performance? (Choose two.)
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
✓
Modify the GSI to include OrderDate as a sort key
The queries are slow because the GSI projects only keys. When querying the GSI, DynamoDB must fetch the full items from the base table (a 'fetch' operation) for each key, which is inefficient. Option C (modifying the GSI to include OrderDate as a sort key) allows the GSI to sort results by order date natively, improving query performance. Option E (changing the GSI projection to include all attributes) avoids the extra fetch by storing all attributes in the GSI, eliminating the need to access the base table. Option A (DAX) caches results but doesn't solve the sorting or projection issue. Option B (increasing read capacity) doesn't address the inefficiency of key-only projection. Option D (using an LSI) is not possible because LSIs require the same partition key as the base table; CustomerID is different from OrderID, so an LSI cannot be used.
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 Accelerator (DAX) for the table
Why it's wrong here
DAX caches data but does not help with sorting or projection issues.
- ✗
Increase the read capacity of the GSI
Why it's wrong here
Increasing read capacity may reduce throttling but does not address the root cause of slow queries.
- ✓
Modify the GSI to include OrderDate as a sort key
Why this is correct
Adding OrderDate as a sort key allows the GSI to return items sorted by order date without additional processing.
- ✗
Use a Local Secondary Index (LSI) instead of a GSI
Why it's wrong here
LSI requires the same partition key as the table (OrderID), not CustomerID.
- ✓
Change the GSI projection to include all attributes
Why this is correct
Projecting all attributes avoids fetching from the base table, reducing latency.
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