Question 765 of 1,711
DEA-C01 Data Operations and Support Practice Question
A data engineer is troubleshooting a slow-running Amazon Redshift query. The query joins several large tables and performs aggregations. The engineer runs EXPLAIN and sees a 'DS_DIST_ALL' step. Which TWO actions will MOST likely improve query performance? (Choose TWO.)
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
✓
Change the distribution style of the tables to DISTSTYLE KEY on the join columns.
The DS_DIST_ALL step in the query plan indicates that data is being broadcast from one node to all others, causing significant network overhead. Option C is correct because changing the distribution style to DISTSTYLE KEY on the join columns ensures that matching rows are co-located on the same node, reducing the need for redistribution. Option E is correct because defining appropriate SORTKEYs based on query predicates allows the query optimizer to use zone maps to skip irrelevant blocks, speeding up scans and aggregations. Option A is incorrect; VACUUM reorganizes data on disk but does not affect distribution. Option B is incorrect; CNAME is a DNS record type, not a Redshift command. Option D is incorrect; increasing nodes might not directly fix the distribution issue and is less targeted than changing distribution style.
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 VACUUM command on all tables.
Why it's wrong here
VACUUM does not fix distribution issues.
- ✗
Use the CNAME command to rename the tables.
Why it's wrong here
CNAME is not a valid Redshift command.
- ✓
Change the distribution style of the tables to DISTSTYLE KEY on the join columns.
Why this is correct
Reduces data redistribution across nodes.
- ✗
Increase the number of nodes in the Redshift cluster.
Why it's wrong here
This adds cost and may not address the root cause.
- ✓
Define appropriate SORTKEYs on the tables based on the query predicates.
Why this is correct
SORTKEYs reduce the amount of data scanned.
Visual reference
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Last reviewed: Jun 20, 2026
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