Apply pattern to make `find_or_create` atomic

app/models/site_statistic.rb

@@ -25,18 +25,21 @@ class SiteStatistic < ActiveRecord::Base
 
     return unless available?
 
-    # we have quite a lot of specs testing migrations, we need this and the rescue to not break them
-    SiteStatistic.transaction(requires_new: true) do
-      SiteStatistic.first_or_create
+    self.fetch # make sure record exists
+
     attribute = self.connection.quote_column_name(raw_attribute)
 
+    # will be running on its own transaction context
     yield(attribute)
   end
-  end
 
   def self.fetch
+    SiteStatistic.transaction(requires_new: true) do
       SiteStatistic.first_or_create!
     end
+  rescue ActiveRecord::RecordNotUnique
+    retry
+  end
 
   def self.available?
     @available_flag ||= ActiveRecord::Migrator.current_version >= REQUIRED_SCHEMA_VERSION