Hi Gavin
Note that Alexander Korotkov already started work in 2013 on a
somewhat similar feature called partial sort:
http://www.postgresql.org/message-id/CAPpHfdscOX5an71nHd8WSUH6GNOCf=V7wgDaTXdDd9=goN-gfA@mail.gmail.com
In particular, see the 2nd patch for KNN sort -- it uses known
bounding boxes from the GiST index for sorting, which in many ways is
similar to min/max BRIN ranges.
> *partial-knn-1.patch*
>
> KNN-GiST provides ability to get ordered results from index, but this order
> is based only on index information. For instance, GiST index contains
> bounding rectangles for polygons, and we can't get exact distance to
> polygon from index (similar situation is in PostGIS). In attached patch,
> GiST distance method can set recheck flag (similar to consistent method).
> This flag means that distance method returned lower bound of distance and
> we should recheck it from heap.
Unfortunatley this work has stalled.
Regards,
Marti
On Sun, Sep 27, 2015 at 11:58 PM, Gavin Wahl <gavinwahl@gmail.com> wrote:
> It seems trivial to accelerate a MAX or MIN query with a BRIN index. You
> just find the page range with the largest/smallest value, and then only scan
> that one. Would that be hard to implement? I'm interested in working on it
> if someone can give me some pointers.
>
> Somewhat harder but still possible would be using BRIN indexes to accelerate
> ORDER BY. This would require a sorting algorithm that can take advantage of
> mostly-sorted inputs. You would sort the page ranges by their minimum or
> maximum value, then feed the sorting algorithm in that order.
