Giving a Symbol here might be a very little bit efficient than giving a String

since the key is goning to be converted to a Symbol later

activerecord/lib/active_record/core.rb

@@ -133,11 +133,11 @@ def self.configurations
       self.filter_attributes = []
 
       def self.connection_handler
-        Thread.current.thread_variable_get("ar_connection_handler") || default_connection_handler
+        Thread.current.thread_variable_get(:ar_connection_handler) || default_connection_handler
       end
 
       def self.connection_handler=(handler)
-        Thread.current.thread_variable_set("ar_connection_handler", handler)
+        Thread.current.thread_variable_set(:ar_connection_handler, handler)
       end
 
       self.default_connection_handler = ConnectionAdapters::ConnectionHandler.new