DEA-C01 Data Operations and Support Practice Question
A company runs a data warehouse on Amazon Redshift. The data engineer notices that some queries are running slowly. Upon reviewing the system tables, the engineer finds that the 'svv_table_info' shows high 'unsorted' percentage for several large tables. What is the MOST effective action to improve 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
✓
Run the VACUUM command on the tables.
VACUUM sorts the data and reclaims space, improving query performance. Option A is wrong because ANALYZE updates statistics but does not sort. Option C is wrong because increasing the number of nodes may help but is not the most direct fix for unsorted data. Option D is wrong because changing distribution style would require recreating the table.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Run the ANALYZE command on the tables.
Why it's wrong here
ANALYZE updates statistics but does not sort data.
- ✓
Run the VACUUM command on the tables.
Why this is correct
VACUUM sorts the data, improving query performance.
- ✗
Change the distribution style of the tables to ALL.
Why it's wrong here
Changing distribution style requires table redesign.
- ✗
Increase the number of nodes in the Redshift cluster.
Why it's wrong here
More nodes help with overall performance but not specifically unsorted data.
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Same concept, more angles
1 more way this is tested on DEA-C01
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company uses Amazon Redshift for its data warehouse. A data engineer notices that queries are running slowly and the system's disk space is nearly full. The engineer runs the STV_PARTITIONS view and sees that many slices have high 'tossed' counts. What does this indicate, and what should the engineer do?
medium- A.The tossed rows are permanent and cannot be reclaimed; the engineer should perform a deep copy to a new table.
- B.The tossed rows indicate that the sort key is not optimal; redefining the sort key will reduce tossed rows.
- C.The tossed rows are due to data skew; redistribute the table on a different distribution key.
- ✓ D.The tossed rows are deleted rows that need to be reclaimed by running VACUUM.
Why D: The STV_PARTITIONS view shows 'tossed' rows, which are rows that have been deleted or updated and are waiting to be reclaimed by a VACUUM operation. High tossed counts indicate wasted disk space, and running VACUUM reclaims that space, improving performance. Option D correctly describes this. Option A is incorrect because tossed rows are not permanent; they can be reclaimed. Option B is incorrect because tossed rows are not related to sort key optimization. Option C is incorrect because tossed rows are not caused by data skew; data skew is about uneven distribution.
JA
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.