DBS-C01 Management and Operations Practice Question
A company is running Amazon Redshift and notices that queries are slow. The administrator runs the STL_ALERT_EVENT_LOG and sees many 'Nested Loop Join' alerts. What is the MOST likely cause?
⚠ Common exam trap
Candidates often confuse distribution keys with sort keys or compression, assuming that poor data organization or storage efficiency directly causes join performance issues, when in fact the root cause is data co-location and the join algorithm selected by the optimizer.
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
✓
Incorrect distribution keys on the tables.
Nested loop joins in Amazon Redshift occur when the query optimizer cannot use a hash join or merge join, often because the data required for the join is not co-located on the same compute nodes. Incorrect distribution keys cause data to be distributed unevenly or in a way that forces large amounts of data to be redistributed across the network, leading to nested loop joins as a fallback. This is the most likely cause because the STL_ALERT_EVENT_LOG specifically flags nested loop joins as a performance issue related to data 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.
- ✗
Insufficient concurrency scaling.
Why it's wrong here
Concurrency scaling affects query queuing.
- ✗
Incorrect sort keys on the tables.
Why it's wrong here
Sort keys affect order, not join method.
- ✗
Insufficient compression on the tables.
Why it's wrong here
Compression affects storage and I/O, not join algorithm.
- ✓
Incorrect distribution keys on the tables.
Why this is correct
Missing dist keys cause large data movement.
Go deeper
Related to this question
About these practice questions
This DBS-C01 question is part of Courseiva's 1,663-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DBS-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 DBS-C01 exam.