DEA-C01 Data Store Management Practice Question
A company uses Amazon DynamoDB for a gaming application. The table has a partition key of 'user_id' and a sort key of 'game_timestamp'. The application frequently queries by 'user_id' and filters by 'game_timestamp' within a specific date range. The queries are slow. The table has a global secondary index (GSI) on 'game_timestamp'. What is the most likely cause of the slow queries?
⚠ Common exam trap
Many candidates assume a GSI is always the solution for slow queries, but the real issue is partition-level throttling from uneven access patterns, which a GSI on a different attribute cannot fix.
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
✓
A hot partition exists due to uneven access pattern on 'user_id'.
The slow queries are most likely caused by a hot partition on the base table. Even though the query uses 'user_id' as the partition key, if a small number of 'user_id' values receive a disproportionate amount of traffic, those specific partitions become overloaded, causing throttling and high latency. The GSI on 'game_timestamp' is not used for these queries because the filter is on the sort key of the base table, and DynamoDB can efficiently query by partition key and filter by sort key without needing a GSI.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The GSI has insufficient read capacity.
Why it's wrong here
Queries are on the base table, not the GSI.
- ✗
The GSI is used instead of the base table for queries on 'user_id'.
Why it's wrong here
Queries on 'user_id' should use the base table, not the GSI.
- ✓
A hot partition exists due to uneven access pattern on 'user_id'.
Why this is correct
If a few 'user_id' values are accessed frequently, they create hot partitions, slowing queries.
- ✗
The sort key is not used in the query.
Why it's wrong here
The query uses the sort key filter, but that should work fine.
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