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Currently, I am administering server with single ASPL.NET website. Website is very realtime, once user opens the page, it gets updated every second. Luckily site is coded by really good guy, and it seems to be working pretty fine.

I am watching Performance Monitor, and average values for previous 10 minutes are:

-143 for Requests / sec

-9.75 - Active Requests

-9.93 - CPU%

My question is - when should I suggest that we scale? Or to add more servers to the cluster? Should I be worried about amount of concurrent HTTP connections to the server (going over limit of concurrent connections that IIS can handle)? Or you think that with these values 100% CPU will be hit before Requests / sec limit?

Can anybody provide metrics as to what are maximum Requests / sec IIS can handle (what are the values from servers you are maintaining)?

EDIT: Also, I would be thankful if experienced administrators can propose other metrics I should follow in Performance Monitor related to monitoring IIS and ASP.NET.

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2 Answers

Can anybody provide metrics as to what are maximum Requests / sec IIS can handle?

As many as it can. You do realize that there is no limit - this basically is asking "ho fast can a car go" and the answer is "as fast as it was build for". So, requests/second says how many requests got handled per second, and that dependson how many requests came in and whether processing was fast enough - which may be cpu limited or not, depending what the cpu does.

9.75 - Active Requests

So you have only 9.75 concurrent requests at that moment in time.

Most important will likely be having a test program open that page itself and measure the time it takes to get an answer. The moment that starts taking longer you may start to develop a problem. Anything else is just a preliminary metrics, no the one you are interested in.

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Thanks for your answer man! I asked for maximum Requests / sec because I wanted to get some metrics from other people who are maintaining high-traffic sites... to know what are the limits. Something like this: plentyoffish.wordpress.com/2007/02/09/… –  kape123 Jun 17 '11 at 9:08
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I've managed to do 4000 RPS on Amazon EC2 c1.medium instance. But this is pretty simple service running. Serving ads to mobile clients. Before any caching applied load tests shown us around 100-200 rps on update requests, and 300-400 rps on SELECT requests.

In a day I've moved caching to Redis server, and now this medium instance is able to serve around 4K requests before CPU cap. And I'm sure there is an possibility to increase this values.

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