IIS7 Integrated Pipeline: Interaction between maxConcurrentRequestsPerCPU and requestsQueueLimit settings

Question

Firstly there\'s a great overview of the IIS7 HTTP request lifecycle and various settings that affect performance here:

ASP.NET Thread Usage on IIS 7.0 and 6.0

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Answer 1

***Is my interpretation correct?

Yes, if you want to execute more than 5000 requests concurrently, you'll need to increase the requestQueueLimit. The requestQueueLimit restricts the total number of requests in the system. Due to its legacy, it is actually the total number of requests in the system, and not the number of requests in some queue. It's goal is to prevent the server from toppling over due to lack of physical memory, virtual memory, etc. When the limit is reached, incoming requests will receive a quick 503 "Server Too Busy" response. By the way, the current number of requests in the system is exposed by the "ASP.NET\Requests Current" performance counter.

***can I disable requestQueueLimit? (set it to zero?)

You can effectively disable it by setting it to a large value, like 50000. You must set the value in the aspnet.config fileI doubt your server can handle 50000 concurrent requests, but if so, then double that. Setting it to zero will not disable it...oddly, it means no more than one request can execute concurrently.

By the way, it looks like there is a bug in v4. For integrated mode, it only successfully reads the value of requestQueueLimit if it is configured in the aspnet.config file as described on MSDN. For some reason, v4 was not reading it from machine.config when I experimented with it a little bit ago.

Answer 2

You might want to check this application's source code. IIS tuner is an open source application which optimizes IIS settings for better performance. On the other hand this page could be useful for your questions.