DBS-C01 Workload-Specific Database Design Practice Question
A company uses Amazon DynamoDB for a high-traffic leaderboard application that updates scores in real-time. The table has partition key 'game_id' and sort key 'player_id'. Queries retrieve top 10 players by score for each game. Which secondary index design is most efficient?
⚠ Common exam trap
Many exam-takers confuse LSIs with GSIs, thinking an LSI can provide a different sort key for global queries, but LSIs are limited to the same partition key as the base table and cannot be used to query across all games.
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 partition key 'game_id' and sort key 'score'
A global secondary index (GSI) with partition key 'game_id' and sort key 'score' allows efficient retrieval of the top 10 players per game by querying a single partition (game_id) and using the sort key to order by score descending. This avoids the 1 MB read limit per partition and provides the necessary ordering without scanning the entire 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.
- ✓
Create a global secondary index (GSI) with partition key 'game_id' and sort key 'score'
Why this is correct
Correct because a GSI with partition key 'game_id' and sort key 'score' enables efficient query per game, ordering by score descending to retrieve top players.
- ✗
Create a global secondary index (GSI) with partition key 'game_id' and sort key 'player_id'
Why it's wrong here
Incorrect because sorting by 'player_id' does not retrieve players by score; you would need to sort after retrieval, which is inefficient.
- ✗
Create a local secondary index (LSI) with sort key 'score'
Why it's wrong here
Incorrect because an LSI must share the same partition key as the base table ('game_id') and cannot be used to query across all games; also, it does not provide a different sort key that orders by score without additional sorting.
- ✗
Do not create any index; use the base table with a scan
Why it's wrong here
Incorrect because scanning the entire table is inefficient and expensive for a high-traffic leaderboard, especially with real-time updates.
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