- A
Network bandwidth saturation between nodes.
Why wrong: Network issues cause 'network' waits, not WLM queuing.
- B
Sorting operations are too expensive.
Why wrong: Expensive sorts cause longer execution times, not queuing.
- C
The number of concurrent queries exceeds the available query slots.
Automatic WLM limits concurrency, and queries queue when exceeded.
- D
Insufficient disk space on the cluster.
Why wrong: Disk space issues cause 'disk full' errors, not WLM queuing.
Question 770 of 1,786
Redshift WLM Queued Time — Concurrency Limits
This DEA-C01 practice question tests your understanding of data store management. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 is troubleshooting an Amazon Redshift cluster that has been experiencing slow query performance. The engineer checks the system tables and finds that many queries are waiting on 'wlm_queued' time. The cluster has 10 nodes and uses automatic WLM. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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 number of concurrent queries exceeds the available query slots.
When queries show 'wlm_queued' time in Amazon Redshift, it indicates they are waiting in the Workload Management (WLM) queue before execution. With automatic WLM, the system dynamically manages concurrency, but if the number of concurrent queries exceeds the available query slots (determined by the cluster's memory and concurrency scaling settings), queries will be queued. This is the most direct cause of 'wlm_queued' wait events, as WLM queues queries when all slots are occupied.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Network bandwidth saturation between nodes.
Why it's wrong here
Network issues cause 'network' waits, not WLM queuing.
- ✗
Sorting operations are too expensive.
Why it's wrong here
Expensive sorts cause longer execution times, not queuing.
- ✓
The number of concurrent queries exceeds the available query slots.
Why this is correct
Automatic WLM limits concurrency, and queries queue when exceeded.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Insufficient disk space on the cluster.
Why it's wrong here
Disk space issues cause 'disk full' errors, not WLM queuing.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse 'wlm_queued' with resource contention (like CPU or I/O), but WLM queuing specifically indicates a concurrency limit, not a performance bottleneck during execution.
Detailed technical explanation
How to think about this question
Automatic WLM in Redshift uses a single queue with a concurrency level that scales based on cluster size and memory, but it does not eliminate queuing entirely. The 'wlm_queued' metric in the STL_WLM_QUERY system table measures the time a query spends waiting for a slot, which can spike during bursty workloads even with auto-scaling. In practice, enabling concurrency scaling can mitigate this by routing queries to transient clusters, but it incurs additional costs.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this DEA-C01 question test?
Data Store Management — This question tests Data Store Management — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The number of concurrent queries exceeds the available query slots. — When queries show 'wlm_queued' time in Amazon Redshift, it indicates they are waiting in the Workload Management (WLM) queue before execution. With automatic WLM, the system dynamically manages concurrency, but if the number of concurrent queries exceeds the available query slots (determined by the cluster's memory and concurrency scaling settings), queries will be queued. This is the most direct cause of 'wlm_queued' wait events, as WLM queues queries when all slots are occupied.
What should I do if I get this DEA-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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