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Did you know there's a "request execution limit" on IIS? It's 3, 10, 25, or unlimited, depending...

Note: This blog post is from 2011. Some content may be outdated--though not necessarily. Same with links and subsequent comments from myself or others. Corrections are welcome, in the comments. And I may revise the content as necessary.
Did you know there's a "request execution limit" on IIS? It's 3, 10, or unlimited, depending on the version of Windows (Vista, 7, 2008) and edition (such as Starter/Home/Basic/Pro/Server).

I'll detail the limits per version/edition below.

I'll also offer a (possibly surprising) workaround that can allow you to get even more requests through IIS, even for a single web site.

(Before I elaborate on that, note that there is a separate issue if you're finding that CF doesn't let you see more than 25 requests at once. That's instead due to a setting in CF/JRun, the maxworkerthreads setting. For more on that, see this blog entry.)

That said, this is a problem which could affect anyone regardless of the app server they may be running behind IIS. (And yes, I do realize that for some, the answer to this problem will be, "see, that's another reason to run Apache." We get that. Let's just focus on this problem for those who choose/have to remain on IIS.)

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Comments
Loved reading this post its good to see the real facts on this, made me rethink my own thoughts on the matter
# Posted By arimidex side effects | 9/5/11 4:58 AM
Can multiple worker processes per application pool cause problems with coldfusion9(jrun connector)?
# Posted By Demar | 10/24/11 4:52 PM
None that I'm aware of, Demar.
I will post again when it is confirmed but using more than one worker process seems to corrupt the IIS-->Jrun communications when used with Fusion-Reactor. If anyone else out there has done any load testing using multiple worker processes with CF9 Enterprise I would love to hear about it.
# Posted By Demar | 10/25/11 12:54 PM
The problem seems to have nothing to do with FusionReactor, it's just that people who have FusionReactor have seen the memory running high via FusionReactor.

I work for FusionReactor and we've helped several customers now with this issue where the protocol (JRPP) between the JRun ISAPI connector and JRun is breaking down causing the web requests to use up huge amounts of memory. FusionReactor does not alter or monitor that protocol in anyway.

Some customers have simply re-installed the JRun connector and the issue hasn't returned. We think that it may be related to mismatched versions of the JRun connector and CF but we cannot confirm that for every case yet. We are aiming to find the issue and report it to Adobe once we understand it.

If we find out more we'll let you know.
# Posted By Darren | 10/26/11 4:59 AM
Darren is correct. After creating new connectors I have not been able to reproduce the problem regardless of the number of application pool processes.
# Posted By demar | 10/27/11 5:40 PM
Very good to hear. Thanks, both of you for sharing your observations.
I read that increasing worker processes per application pool (web garden) does not affect the peformance and it's recommended to be 1 (default setting).
# Posted By ganaysa | 9/2/14 7:10 AM
@ganaysa, let me try to restate things: I too could make a case against using more than one worker process per app pool, agreeing that it doesn't "affect performance" for the better (in general, and especially with respect to CF), though we don't want to leave the impression that no one would ever benefit.

But to be clear, I was very specific in my reasoning for suggesting its use here: I was saying it's a way to get around the built-in limitation that IIS has--in some editions of Windows---to the number of requests that can be run concurrently.

So I would stand by my recommendation that even despite your assertion (which I would otherwise agree with) that in this specific case it COULD well "affect performance" positively.

Hope that's helpful.
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