Replace self-rolled statsd instrumention with localshred/nsa (#5118)

config/initializers/statsd.rb

@@ -1,18 +1,15 @@
 # frozen_string_literal: true
-RESERVED_CHARACTERS_REGEX = /[\:\|\@]/
 
-StatsD.prefix              = 'mastodon'
-StatsD.default_sample_rate = 1
+if ENV['STATSD_ADDR'].present?
+  host, port = ENV['STATSD_ADDR'].split(':')
 
-def clean_name(str)
-  str.gsub('::', '.').gsub(RESERVED_CHARACTERS_REGEX, '_')
-end
-
-ActiveSupport::Notifications.subscribe(/performance/) do |name, _start, _finish, _id, payload|
-  action      = payload[:action] || :increment
-  measurement = payload[:measurement]
-  value       = payload[:value]
-  key_name    = clean_name("#{name}.#{measurement}")
-
-  StatsD.send(action.to_s, key_name, (value || 1))
+  statsd = ::Statsd.new(host, port)
+  statsd.namespace = ['Mastodon', Rails.env].join('.')
+
+  ::NSA.inform_statsd(statsd) do |informant|
+    informant.collect(:action_controller, :web)
+    informant.collect(:active_record, :db)
+    informant.collect(:cache, :cache)
+    informant.collect(:sidekiq, :sidekiq)
+  end
 end