Quick Answer
The answer is to run the VACUUM command. This is correct because in Amazon Redshift, UPDATE and DELETE operations do not physically remove old data; they mark rows as deleted, leaving behind "ghost" rows that consume storage and degrade query performance. The VACUUM command reclaims that disk space by permanently removing those rows and re-sorting the remaining data according to the table’s sort keys, which directly reduces storage usage and improves scan efficiency. On the AWS Certified Data Engineer Associate DEA-C01 exam, this concept tests your understanding of Redshift’s MVCC architecture and the difference between logical and physical deletes. A common trap is confusing VACUUM with ANALYZE—remember that ANALYZE updates statistics but does not free space. For a memory tip, think of VACUUM as a "vacuum cleaner" that sucks up the dead row debris left behind by updates and deletes, leaving your storage clean and your queries fast.
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 data engineer notices that an Amazon Redshift cluster’s storage usage is increasing rapidly due to many UPDATE and DELETE operations. The engineer needs to reclaim storage space and improve query performance. Which action should be taken?
Run VACUUM command
VACUUM reclaims disk space and re-sorts rows.
UNLOAD the table to S3 and reload
Why wrong: Unloading and reloading is inefficient and not best practice.
Increase cluster node count
Why wrong: Scaling out does not reclaim space from existing data.
Run ANALYZE command
Why wrong: ANALYZE updates statistics, does not reclaim space.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Run VACUUM command
The VACUUM command in Amazon Redshift reclaims disk space occupied by deleted or updated rows and re-sorts the data according to the table's sort keys. This directly addresses the storage increase from UPDATE/DELETE operations and improves query performance by restoring the physical order of rows, which reduces the number of blocks scanned.
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.
Run VACUUM command
Why this is correct
VACUUM reclaims disk space and re-sorts rows.
Related concept
Read the scenario before looking for a memorised answer.
UNLOAD the table to S3 and reload
Why it's wrong here
Unloading and reloading is inefficient and not best practice.
Increase cluster node count
Why it's wrong here
Scaling out does not reclaim space from existing data.
Run ANALYZE command
Why it's wrong here
ANALYZE updates statistics, does not reclaim space.
Common exam traps
The trap here is that candidates confuse ANALYZE with VACUUM, thinking updating statistics will also reclaim storage, when in fact ANALYZE only refreshes metadata for the query optimizer and has no effect on physical storage.
Detailed technical explanation
Amazon Redshift stores data in 1 MB blocks on disk, and UPDATE/DELETE operations mark rows as deleted but do not immediately free the blocks. The VACUUM command performs a deep copy of remaining rows into new blocks, skipping the deleted ones, and then drops the old blocks, which both reclaims space and re-establishes sort order. In practice, a full VACUUM can be resource-intensive on large tables, so engineers often schedule it during maintenance windows or use VACUUM DELETE ONLY to focus on space reclamation without re-sorting.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
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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: Run VACUUM command — The VACUUM command in Amazon Redshift reclaims disk space occupied by deleted or updated rows and re-sorts the data according to the table's sort keys. This directly addresses the storage increase from UPDATE/DELETE operations and improves query performance by restoring the physical order of rows, which reduces the number of blocks scanned.
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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