DEA-C01 Data Store Management Practice Question
A data engineering team is managing an Amazon Redshift cluster that is used for BI reporting. The cluster has a mix of large tables (some over 1 TB) and many smaller tables. The team notices that queries on a large fact table are slow. The fact table is distributed using KEY distribution on the customer_id column, which has high cardinality. The team wants to improve query performance. They have the option to change the distribution style and sort key. Which redesign should they implement?
⚠ Common exam trap
It's easy for candidates to assume KEY distribution on a high-cardinality column is optimal for large tables, but they overlook that even high-cardinality keys can cause severe data skew if the distribution key values are not uniformly distributed across nodes, leading to poor query performance.
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
✓
Change the distribution style to EVEN and set the sort key to a date column used in WHERE clauses.
Using EVEN distribution ensures data is evenly distributed across all nodes, avoiding data skew that can occur with KEY distribution on a high-cardinality column like customer_id. Setting the sort key to a date column used in WHERE clauses enables range-restricted scans, significantly reducing the amount of data scanned for common BI queries that filter by date. This combination improves query performance by maximizing parallelism and minimizing I/O.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Keep the distribution style as AUTO and set the sort key to customer_id.
Why it's wrong here
AUTO may not provide optimal distribution.
- ✗
Change the distribution style to ALL and set the sort key to customer_id.
Why it's wrong here
ALL is not suitable for large tables.
- ✗
Change the distribution style to KEY on a different column with high cardinality.
Why it's wrong here
High cardinality may cause skew.
- ✓
Change the distribution style to EVEN and set the sort key to a date column used in WHERE clauses.
Why this is correct
EVEN distributes evenly; sort key on date improves query performance.
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