DBS-C01 Workload-Specific Database Design Practice Question
A media company stores video metadata in Amazon DynamoDB. Each record has a partition key of video_id and a sort key of uploaded_timestamp. The application frequently queries videos by genre and upload date. The access pattern is read-heavy with occasional writes. The table is provisioned with 3000 RCUs and 1000 WCUs. The company notices that queries by genre are slow and consume many RCUs. Which design change should be made to optimize for this workload?
⚠ Common exam trap
Candidates often confuse LSIs and GSIs, incorrectly assuming an LSI can change the partition key, when in fact LSIs must share the main table's partition key, making them unsuitable for querying by a different attribute like genre.
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 genre as partition key and uploaded_timestamp as sort key.
Creating a Global Secondary Index (GSI) with genre as the partition key and uploaded_timestamp as the sort key allows efficient querying by genre and date without scanning the entire table. This directly supports the access pattern, reducing RCU consumption by using index key lookups instead of full table scans. The GSI is ideal for read-heavy workloads with occasional writes, as it offloads query traffic from the main table.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use DynamoDB Accelerator (DAX) to cache query results.
Why it's wrong here
DAX caches results but does not improve the efficiency of the query pattern itself.
- ✗
Create a local secondary index (LSI) with genre as sort key and uploaded_timestamp as partition key.
Why it's wrong here
LSI must have the same partition key as the base table; genre cannot be the partition key.
- ✗
Increase the provisioned RCUs to 6000.
Why it's wrong here
Increasing RCUs does not reduce the cost of inefficient queries; it only provides more capacity.
- ✓
Create a global secondary index (GSI) with genre as partition key and uploaded_timestamp as sort key.
Why this is correct
A GSI with genre as partition key allows efficient queries by genre and date.
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