No need for memoization

At this point the application name can't change.

Author: rafaelfranca

activerecord/lib/active_record/railtie.rb

@@ -347,7 +347,7 @@ class Railtie < Rails::Railtie # :nodoc:
       config.after_initialize do
         if app.config.active_record.query_log_tags_enabled
           ActiveRecord::QueryLogs.taggings.merge!(
-            application:  -> { @application_name ||= Rails.application.class.name.split("::").first },
+            application:  Rails.application.class.name.split("::").first,
             pid:          -> { Process.pid },
             socket:       -> { ActiveRecord::Base.connection_db_config.socket },
             db_host:      -> { ActiveRecord::Base.connection_db_config.host },