This adds a new optional support function to the GiST access method: sortsupport. If it is defined, the GiST index is built by sorting all data to the order defined by the sortsupport's comparator function, and packing the tuples in that order to GiST pages. This is similar to how B-tree index build works, and is much faster than inserting the tuples one by one. The resulting index is smaller too, because the pages are packed more tightly, upto 'fillfactor'. The normal build method works by splitting pages, which tends to lead to more wasted space. The quality of the resulting index depends on how good the opclass-defined sort order is. A good order preserves locality of the input data. As the first user of this facility, add 'sortsupport' function to the point_ops opclass. It sorts the points in Z-order (aka Morton Code), by interleaving the bits of the X and Y coordinates. Author: Andrey Borodin Reviewed-by: Pavel Borisov, Thomas Munro Discussion: https://www.postgresql.org/message-id/1A36620E-CAD8-4267-9067-FB31385E7C0D%40yandex-team.ru