request_profiler

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= Request Profiler

+request_profiler+ is a rack middleware that allows you to profile rack requests using {ruby-prof}[https://github.com/rdp/ruby-prof]. It sits out of the way until it's triggered using a specific request parameter. Once triggered, it will profile the request and dump a log file.

== Setup

After the gem is installed, it's used in the same way any rack middleware is set up. In Rails, you'd probably want to do something like this:

config.middleware.use "Rack::RequestProfiler"

+request_profiler+ takes a few optional parameters:

:printer:: the ruby-prof printer to use. Defaults to RubyProf::GraphPrinter.

:exclude:: a list of regexes (like [/Integer#times]) that will not appear in the profile log. This is most commonly used for methods that take a block, where you don't care how much time was spent in the method itself.

:path:: the path to write the log files to. If +request_profiler+ is running under Rails, this defaults to Rails.root/tmp/performance, otherwise it defaults to $TMPDIR/performance.

== Using +request_profiler+

When you get to the point where you'd like to profile a request, you just add profile_request=true to the end of your request's query string. By default, this will use the RubyProf::PROCESS_TIME profiler. If you'd like to use a different profiler, you can specify the profiler class instead of +true+ in the query string. For example,

profile_request=memory

will use the RubyProf::MEMORY profiler. Note that the profilers other than +PROCESS_TIME+ and +WALL_TIME+ require a patched ruby interpreter, as mentioned in the ruby-prof documentation. REE should work out of the box, but as far as I know, these patches don't yet exist for ruby 1.9.

== Bugs Under Ruby 1.9.2

+ruby_prof+ uses a ruby method called +set_trace_func+, which tends to crash under ruby 1.9.2. I have an experimental patch which backports the fix in the 1.9.3 branch to 1.9.2, and adjusts the stack depth threshhold ruby uses, which fixes some other interpreter crashes I was seeing. If you run into similar issues, you should grab the patch located under +patches/set_trace_func_fix192.patch+. With {rvm}[http://rvm.beginrescueend.com/], it's as simple as

rvm install 1.9.2p0 --patch /path/to/set_trace_func_fix192.patch