DEA-C01 Data Operations and Support Practice Question
A data engineer is troubleshooting a slow Amazon Redshift query. The query scans a large table with interleaved sort keys. The engineer notices that the query plan shows a sequential scan instead of a range-restricted scan. What is the MOST likely reason?
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
✓
The table has not been vacuumed and reindexed after large data loads.
Interleaved sort keys require periodic VACUUM REINDEX to maintain sort order. Without it, Redshift may fall back to sequential scans. Option B is incorrect because DISTKEY affects data distribution, not sort key usage. Option C is incorrect because compression does not prevent range-restricted scans. Option D is incorrect because WLM queue slots affect concurrency, not scan type.
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 table has not been vacuumed and reindexed after large data loads.
Why this is correct
Without VACUUM REINDEX, interleaved sort keys lose effectiveness, causing sequential scans.
- ✗
The table has a poor distribution key (DISTKEY) causing data skew.
Why it's wrong here
DISTKEY affects data distribution across nodes, not sort key effectiveness.
- ✗
The table uses compression encodings that prevent range-restricted scans.
Why it's wrong here
Compression does not prevent range-restricted scans.
- ✗
The workload management (WLM) queue is configured with too few query slots.
Why it's wrong here
WLM queue configuration affects concurrency, not scan type.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.