Redis instrumentation

gistfile1.rb

::Redis::Client.class_eval do

  # Support older versions of Redis::Client that used the method
  # +raw_call_command+.
  call_method = ::Redis::Client.new.respond_to?(:call) ? :call : :raw_call_command

  def call_with_stats_trace(*args, &blk)
    method_name = args[0].is_a?(Array) ? args[0][0] : args[0]
    start = Time.now
    begin
      call_without_stats_trace(*args, &blk)
    ensure
      METRICS.timing("#{Thread.current[:stats_context] || 'wild'}.redis.#{method_name.to_s.upcase}.query_time", 
                       ((Time.now - start) * 1000).round, 1) rescue nil
    end
  end

  alias_method :call_without_stats_trace, call_method
  alias_method call_method, :call_with_stats_trace

end if defined?(::Redis::Client)

This is in reference to http://www.mikeperham.com/2012/08/25/using-statsd-with-rails/ and based on https://github.com/evanphx/newrelic-redis

Apply the same approach to instrument call_pipelined.

Thread.current[:stats_context] is used to set a context such as the name of an API endpoint or "http.#{controller_name}.#{action}" so my Redis instrumentation reports are scoped and I can compare the response time of a request with the time spent in AR, Redis and in external HTTP requests. In Graphite, you can look for data using wild cards and therefore find all the instrumentation Redis stats.

This is the way that I prefer to monkey patch things. I find it very rare where Module#alias_method is actually required.

module StatsCollector
  call_method = ::Redis::Client.method_defined?(:call) ? :call : :raw_call_method
  define_method(call_method) do |*args, *blk|
    method_name = args[0].is_a?(Array) ? args[0][0] : args[0]
    start = Time.now
    begin
      super(*args, &blk)
    ensure
      METRICS.timing("#{Thread.current[:stats_context] || 'wild'}.redis.#{method_name.to_s.upcase}.query_time",
                       ((Time.now - start) * 1000).round, 1) rescue nil
    end
  end
end

redis = Redis.new(:host => '127.0.0.1', :port => 6379, :password => 'xyz')
redis.extend(StatsCollector)
redis.set('foo', '1')