Quick Answer
The answer is to run SELECT * FROM SVV_TABLE_INFO ORDER BY unsorted DESC;. This diagnostic query is correct because the SVV_TABLE_INFO system view exposes an unsorted column that reports the percentage of rows not in sort key order for each table. When a table accumulates unsorted rows, Redshift’s zone maps become less effective, forcing more scans and degrading query performance—so ordering by unsorted descending immediately surfaces the worst offenders. On the AWS Certified Data Engineer Associate DEA-C01 exam, this question tests your ability to troubleshoot performance using system views rather than guessing; a common trap is confusing SVV_TABLE_INFO with STL_SCAN or STV_TBL_PERM, which lack the unsorted metric. Remember the mnemonic: “Unsorted DESC puts the worst first.”
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 is experiencing slow query performance. The engineer suspects that tables are not properly sorted. Which diagnostic query should the engineer run to identify unsorted rows?
SELECT * FROM SVV_TABLE_INFO ORDER BY unsorted DESC;
SVV_TABLE_INFO shows unsorted rows for each table.
SELECT * FROM PG_CATALOG;
Why wrong: PG_CATALOG is a schema, not a view for unsorted rows.
SELECT * FROM STV_TBL_PERM;
Why wrong: STV_TBL_PERM is not a valid system view.
SELECT * FROM STL_LOAD_ERRORS;
Why wrong: This view shows errors during data loads, not unsorted rows.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
SELECT * FROM SVV_TABLE_INFO ORDER BY unsorted DESC;
The `SVV_TABLE_INFO` system view in Amazon Redshift provides metadata about each table, including the `unsorted` column which shows the percentage of unsorted rows. By ordering by `unsorted DESC`, the engineer can quickly identify tables with the highest proportion of unsorted data, which directly impacts query performance due to inefficient zone maps and scan pruning.
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.
SELECT * FROM SVV_TABLE_INFO ORDER BY unsorted DESC;
Why this is correct
SVV_TABLE_INFO shows unsorted rows for each table.
Related concept
Read the scenario before looking for a memorised answer.
SELECT * FROM PG_CATALOG;
Why it's wrong here
PG_CATALOG is a schema, not a view for unsorted rows.
SELECT * FROM STV_TBL_PERM;
Why it's wrong here
STV_TBL_PERM is not a valid system view.
SELECT * FROM STL_LOAD_ERRORS;
Why it's wrong here
This view shows errors during data loads, not unsorted rows.
Common exam traps
The trap here is that candidates may confuse `SVV_TABLE_INFO` with `STV_TBL_PERM` (which shows block counts) or `STL_LOAD_ERRORS` (which is for load debugging), missing that only `SVV_TABLE_INFO` exposes the `unsorted` column specifically designed for sort health analysis.
Trap categories for this question
Command / output trap
This view shows errors during data loads, not unsorted rows.
Detailed technical explanation
Redshift stores data in 1 MB blocks, and each block's metadata (min/max values) is used for zone map pruning during scans. When a table is poorly sorted, blocks contain overlapping value ranges, reducing the effectiveness of pruning and forcing more blocks to be read. The `unsorted` column in `SVV_TABLE_INFO` is calculated as the ratio of rows that are not in sort key order to total rows, and a high percentage (e.g., >10%) often indicates that a `VACUUM SORT ONLY` operation is needed to restore sort order and improve query performance.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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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: SELECT * FROM SVV_TABLE_INFO ORDER BY unsorted DESC; — The `SVV_TABLE_INFO` system view in Amazon Redshift provides metadata about each table, including the `unsorted` column which shows the percentage of unsorted rows. By ordering by `unsorted DESC`, the engineer can quickly identify tables with the highest proportion of unsorted data, which directly impacts query performance due to inefficient zone maps and scan pruning.
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
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