On Fri, Mar 8, 2019 at 9:15 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> David Rowley <david.rowley@2ndquadrant.com> writes:
> > [ v9-0001-Allow-Append-to-be-used-in-place-of-MergeAppend-f.patch ]
>
> I think you should remove all that
> and restrict this optimization to the case where all the subpaths are
> natively ordered --- if we have to insert Sorts, it's hardly going to move
> the needle to worry about simplifying the parent MergeAppend to Append.
This can be a huge win for queries of the form "ORDER BY partkey LIMIT
x". Even if the first subpath(s) aren't natively ordered, not all of
the sorts should actually be performed.