Caused by lack of available threads, this can occur in periods of high CPU utilization particularly when parallelism is involved, excessive blocking and excessive database mirrors or Availability Group Replicas

Resolved by


Suggested solutions

  1. Run Profiler/Trace/Extended Events to determine if blocked queries exist. Optimize or rewrite blocking queries
  2. Optimize parallel queries
  3. Decrease the number of database mirrors or Availability Groups if the count exceeds the limits specified in the link below

Additional research

AlwaysOn Availability Groups Worker Thread Consumption
Troubleshooting THREADPOOL Waits

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