ASP.NET: HttpModule performance

Question

I've implemented an HttpModule that intercepts the Response stream of every request and runs a half dozen to a dozen Regex.Replace()s on each text/html-typed response. I'm concerned about how much of a performance hit I'm incurring here. What's a good way to find out? I want to compare speed with and without this HttpModule running.

Answer 1

Http module is just common piece of code, so you can measure time of execution of this particular regex replace stuff. It is enough. Have a set of typical response streams as input of your stress test and measure executing of the replace using Stopwatch class. Consider also RegexOptions.Compiled switch.

Answer 2

Here are a few ideas:

1. Add some Windows performance counters, and use them to measure and report average timing data. You might also increment a counter only if the time measurement exceeds a certain threshold. and
2. Use tracing combined with Failed Request Tracing to collect and report timing data. You can also trigger FRT reports only if page execution time exceeds a threshold.
3. Write a unit test that uses the Windows OS clock to measure how long your code takes to execute.
4. Add a flag to your code that you can turn on or off with a test page to enable or disable your regex code, to allow easy A/B testing.
5. Use a load test tool like WCAT to see how many page requests per second you can process with and without the code enabled.

Answer 3

I've a few of these that hook into the Response.Filter stream pipeline to provide resource file integration, JS/CSS packing and rewriting of static files to absolute paths.

As long as you test your regexes in RegexBuddy for speed over a few million iterations, ensure you use RegexOptions.Compiled, and remember that often the quickest and most efficient technique is to use a regex to broadly identify matches and then use C# to hone that to exactly what you need.

Make sure you're also caching and configuration that you rely upon.

We've had a lot of success with this.