Re: Optimizer sorting an already sorted result

"Gurjeet Singh" <singh.gurjeet@gmail.com> writes:
> In the plan below, we can see that the optimizer is sorting an already
> sorted result. It seems to forget the sort order across the UNIQUE node. My
> question is, do we make any attempts in the optimizer to remember the sort
> order of a result, to avoid any further sorting on same sort-key? If not,
> can we do something about it?

Per the comment in create_unique_path:
   /*    * Treat the output as always unsorted, since we don't necessarily have    * pathkeys to represent it.    */
pathnode->path.pathkeys= NIL;
 

No doubt this could be improved, but I'm unsure about the effort/reward
ratio.
        regards, tom lane