using the connection pool while visiting

lib/arel/tree_manager.rb

@@ -15,7 +15,7 @@ def to_dot
     end
 
     def to_sql
-      visitor.accept @head
+      @visitor.accept @head
     end
 
     def initialize_copy other

lib/arel/visitors/to_sql.rb

@@ -9,8 +9,10 @@ def initialize engine
       end
 
       def accept object
-        @connection = @engine.connection
-        visit object
+        @engine.connection_pool.with_connection do |conn|
+          @connection = conn
+          visit object
+        end
       end
 
       private