This DEA-C01 practice question tests your understanding of data store management. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company is running a data warehouse on Amazon Redshift. The data engineering team notices that query performance has degraded over time. They suspect that data distribution is causing excessive data movement between nodes. The table is joined frequently on the customer_id column. Which column should be chosen as the distribution key to optimize join performance?
AUTO distribution
Why wrong: AUTO may not select the join column.
customer_id
Distributing on the join column reduces data movement.
order_date
Why wrong: Date columns often cause data skew.
EVEN distribution
Why wrong: Even distribution does not collocate data for joins.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
customer_id
The correct answer is B (customer_id) because Redshift distributes data across nodes based on the distribution key. When two tables are joined on customer_id, using it as the distribution key ensures that matching rows from both tables are co-located on the same node, eliminating the need for data redistribution (broadcast or shuffle) during the join. This minimizes network traffic and reduces query latency, directly addressing the performance degradation caused by excessive data movement.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
AUTO distribution
Why it's wrong here
AUTO may not select the join column.
customer_id
Why this is correct
Distributing on the join column reduces data movement.
Related concept
Read the scenario before looking for a memorised answer.
order_date
Why it's wrong here
Date columns often cause data skew.
EVEN distribution
Why it's wrong here
Even distribution does not collocate data for joins.
Common exam traps
The trap here is that candidates may choose EVEN distribution (D) thinking it balances data evenly, but they overlook that it causes maximum data movement for joins, while AUTO distribution (A) seems safe but does not guarantee co-location for the specific join column.
Detailed technical explanation
Under the hood, Redshift uses a hash-based distribution strategy: when a distribution key is specified, the system applies a hash function to the key value to determine which slice (node) stores the row. For joins on the same key, Redshift can perform a collocated join without moving data between nodes. A real-world scenario is a star schema with a large fact table joined to a dimension table on customer_id; using customer_id as the distribution key for both tables ensures that all rows for a given customer reside on the same node, drastically reducing inter-node traffic.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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FAQ
Data Store Management — This question tests Data Store Management — Read the scenario before looking for a memorised answer..
The correct answer is: customer_id — The correct answer is B (customer_id) because Redshift distributes data across nodes based on the distribution key. When two tables are joined on customer_id, using it as the distribution key ensures that matching rows from both tables are co-located on the same node, eliminating the need for data redistribution (broadcast or shuffle) during the join. This minimizes network traffic and reduces query latency, directly addressing the performance degradation caused by excessive data movement.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
This DEA-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DEA-C01 exam.
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