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Profiling Puppet

Puppet is a beast. Puppet is at times a very slow beast. Maybe we can find what is making it slow and fix it.

Coarse Grained Profiling

There is a built-in system of profiling that can be used to identify some slow spots. This can only work with code that is explicitly instrumented, which, at the time of this writing, is primarily the compiler. To enable profiling there are several options:

  • To profile every request on the master add --profile to your master's startup.
  • To profile a single run for an agent add --profile to your agent's options for that run.
  • To profile a masterless run add --profile to your puppet apply options.

The timing information will be output to the logs and tagged with the word "PROFILE".

For the agent there is actually a second system: evaltrace. You can enable this on the agent by passing it --evaltrace. Timing information for each resource will be output to the logs.

Using a Ruby Profiler

For much finer grained profiling, you'll want to use ruby-prof. Once you have the gem installed you can either modify the code to profile a certain section (using RubyProf.profile) or run the master with ruby-prof by adding use Rack::RubyProf, :path => '/temp/profile' to the config.ru for your master.

Running the Benchmarks

Puppet has a number of benchmark scenarios to pinpoint problems in specific, known, use cases. The benchmark scenarios live in the benchmarks directory.

To run a scenario you do:

bundle exec rake benchmark:<scenario_name>

If you have ruby-prof installed you can get a calltrace of the benchmark scenario by running:

bundle exec rake benchmark:<scenario_name>:profile

The calltrace file is viewable with kcachegrind.