DEA-C01 Data Operations and Support Practice Question
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?
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 tossed rows are deleted rows that need to be reclaimed by running VACUUM.
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.
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 tossed rows are permanent and cannot be reclaimed; the engineer should perform a deep copy to a new table.
Why it's wrong here
Tossed rows can be reclaimed by VACUUM; deep copy is an alternative but not the first action.
- ✗
The tossed rows indicate that the sort key is not optimal; redefining the sort key will reduce tossed rows.
Why it's wrong here
Tossed rows are related to DELETE/UPDATE operations, not sort keys.
- ✗
The tossed rows are due to data skew; redistribute the table on a different distribution key.
Why it's wrong here
Data skew is shown by uneven slice sizes, not tossed counts.
- ✓
The tossed rows are deleted rows that need to be reclaimed by running VACUUM.
Why this is correct
VACUUM removes deleted rows and reclaims disk space, improving query performance.
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