Re: Use LIMIT instead of Unique for DISTINCT when all distinct pathkeys are redundant

On Thu, 13 Oct 2022 at 21:17, Richard Guo <guofenglinux@gmail.com> wrote:
>
> On Thu, Oct 13, 2022 at 2:48 PM David Rowley <dgrowleyml@gmail.com> wrote:
>> To stop the planner from adding that final sort, I opted to hack the
>> LimitPath's pathkeys to say that it's already sorted by the
>> PlannerInfo's sort_pathkeys.  That feels slightly icky, but it does
>> seem a little wasteful to initialise a sort node on every execution of
>> the plan to sort a single tuple.
>
>
> I don't get how this plan comes out. It seems not correct because Limit
> node above an unsorted path would give us an unpredictable row.

Actually, you're right. That manual setting of the pathkeys is an
unneeded remanent from a bug I fixed before sending out v2.  It can
just be removed.

I've attached the v3 patch.