DEA-C01 Data Operations and Support Practice Question
This DEA-C01 practice question tests your understanding of data operations and support. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 data engineer is troubleshooting a slow Amazon Redshift query that joins a large fact table with several dimension tables. The EXPLAIN plan shows a hash join on the distribution key, but the query still runs slowly. The fact table is distributed by KEY(column_x) and the dimension tables are distributed ALL. The engineer notices that the fact table has a high number of rows with the same value in column_x. What is the most likely cause of the slow performance?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The fact table's distribution key column has data skew, causing uneven data distribution across nodes.
Option A is correct because data skew in the distribution key column_x causes some slices to hold a disproportionate number of rows, leading to uneven workload distribution during the hash join. The EXPLAIN plan shows a hash join on the distribution key, which should be efficient if data is evenly distributed, but skew forces the node with the most rows to become a bottleneck, slowing the entire query.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 fact table's distribution key column has data skew, causing uneven data distribution across nodes.
Why this is correct
Skew leads to some nodes doing more work, slowing the query.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The dimension tables should be distributed by KEY instead of ALL.
Why it's wrong here
ALL distribution is usually better for dimension tables.
✗
The Redshift cluster does not have enough disk space.
Why it's wrong here
Disk space might cause errors but not slow performance in this context.
✗
The fact table does not have a sort key.
Why it's wrong here
Sort keys help with range-restricted scans, not join skew.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume a hash join on the distribution key is always optimal, overlooking that data skew in the distribution key itself can negate the benefit and cause severe performance degradation.
Detailed technical explanation
How to think about this question
In Amazon Redshift, hash joins on the distribution key are most efficient when data is evenly distributed across slices; skew causes some slices to process far more rows, leading to straggler nodes that delay query completion. The distribution key column_x with high duplicate values exacerbates skew because all rows with the same value land on the same slice, creating a hot spot. Real-world scenarios like a fact table with a 'country' column where most rows are 'USA' can cause severe skew, requiring redistribution or re-evaluation of the distribution key.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Data Operations and Support — This question tests Data Operations and Support — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The fact table's distribution key column has data skew, causing uneven data distribution across nodes. — Option A is correct because data skew in the distribution key column_x causes some slices to hold a disproportionate number of rows, leading to uneven workload distribution during the hash join. The EXPLAIN plan shows a hash join on the distribution key, which should be efficient if data is evenly distributed, but skew forces the node with the most rows to become a bottleneck, slowing the entire query.
What should I do if I get this DEA-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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