Prepopulate Hash of statement types.

This should hopefully solve an error we've been seeing in concurrent systems
that results in trying to insert into a Hash during iteration.

lib/active_record_stats.rb

@@ -3,6 +3,9 @@
 require 'statsd-instrument'
 
 module ActiveRecordStats
+  STATEMENT_KEYS = %w[BEGIN COMMIT DELETE EXPLAIN INSERT
+    RELEASE ROLLBACK SAVEPOINT SELECT UPDATE WITH].freeze
+
   def self.statement_type(sql)
     return if sql.nil?
 
@@ -12,4 +15,10 @@ def self.statement_type(sql)
     type = cleaned.split(' ', 2).first
     type.try(:upcase)
   end
+
+  def self.statement_hash
+    hash = {}
+    STATEMENT_KEYS.each { |k| hash[k] = 0 }
+    hash
+  end
 end

lib/active_record_stats/rack_middleware.rb

@@ -14,7 +14,7 @@ def initialize(app)
     end
 
     def call(env)
-      totals  = {}
+      totals  = ActiveRecordStats.statement_hash
       db_time = 0
 
       gather_sql = ->(_name, _started_at, _finished_at, _unique_id, payload) {

lib/active_record_stats/resque_plugin.rb

@@ -3,7 +3,7 @@
 module ActiveRecordStats
   module ResquePlugin
     def around_perform_active_record_stats(*args, &block)
-      totals = {}
+      totals = ActiveRecordStats.statement_hash
 
       gather_sql = ->(_name, _started_at, _finished_at, _unique_id, payload) {
         return if payload[:name] == 'SCHEMA' || payload[:sql].blank?

lib/active_record_stats/sidekiq_server_middleware.rb

@@ -3,8 +3,8 @@
 module ActiveRecordStats
   class SidekiqServerMiddleware
     def call(worker, job, queue)
-      totals = {}
-
+      totals = ActiveRecordStats.statement_hash
+      
       gather_sql = ->(_name, _started_at, _finished_at, _unique_id, payload) {
         return if payload[:name] == 'SCHEMA' || payload[:sql].blank?
         return unless type = ActiveRecordStats.statement_type(payload[:sql])