Hi @aspx ,

Microsoft has a performance counter to monitor IIS and asp.net application performance. You can use it to monitor request queue length by following this article.

HTTP Service Request Queues (CurrentQueueSize): The request count in the IIS queue

If you find this value is always 0, that means there's no request in the queue. Each request can be handled immediately on IIS. Though you set queue length 15 to limit it, application pool can create multiple work processes to handle requests. And each work process can create multiple threads to handle requests. Only when there's no more free threads and work processes, request will reach the queue to wait.

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Best regards, Bruce Zhang