- log warnings if logger methods are called outside of the current log

level.

  Enable it with PROFILE_BAD_LOG_CALLS=1 in env.

  Supporting research here:
  https://github.com/jordansissel/experiments/tree/master/ruby/logger-string-vs-block

lib/logstash/runner.rb

@@ -16,6 +16,41 @@ require "logstash/namespace"
 require "logstash/program"
 require "logstash/util"
 
+if ENV["PROFILE_BAD_LOG_CALLS"]
+  # Set PROFILE_BAD_LOG_CALLS=1 in your environment if you want
+  # to track down logger calls that cause performance problems
+  #
+  # Related research here:
+  #   https://github.com/jordansissel/experiments/tree/master/ruby/logger-string-vs-block
+  #
+  # Basically, the following is wastes tons of effort creating objects that are
+  # never used if the log level hides the log:
+  #
+  #     logger.debug("something happend", :what => Happened)
+  #
+  # This is shown to be 4x faster:
+  #
+  #     logger.debug(...) if logger.debug?
+  #
+  # I originally intended to use RubyParser and SexpProcessor to
+  # process all the logstash ruby code offline, but it was much
+  # faster to write this monkeypatch to warn as things are called.
+  require "cabin/mixins/logger"
+  module Cabin::Mixins::Logger
+    LEVELS.keys.each do |level|
+      m = "original_#{level}".to_sym
+      predicate = "#{level}?".to_sym
+      alias_method m, level
+      define_method(level) do |*args|
+        if !send(predicate)
+          warn("Unconditional log call", :location => caller[0])
+        end
+        send(m, *args)
+      end
+    end
+  end
+end
+
 class LogStash::Runner
   include LogStash::Program