Question 770 of 1,711
DEA-C01 Data Store Management Practice Question
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?
⚠ Common exam trap
Watch out — candidates often 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.
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.
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.
- ✗
Insufficient disk space on the cluster.
Why it's wrong here
Disk space issues cause 'disk full' errors, not WLM queuing.
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Last reviewed: Jul 4, 2026
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