Hi Darafei, Thanks for your reply.
However, I still don't get the full picture of this. Let me make my question more clear. First of all, in the *`gistproc.c <https://github.com/postgres/postgres/blob/master/src/backend/access/gist/gistproc.c#L1761>`* of Postgres, it shows that the `abbreviate` attributes should be set before the `abbrev_converter` defined. So I would like to know where to define a `SortSupport` structure with `abbreviate` is `true`. Secondly, in the support functions of internal data type `Point`, the `abbrev_full_copmarator` just z-order hash the point first like the `abbrev_converter` doing and then compare the hash value. So I don't know the difference between `full_comparator` and `comparator` after `abbrev_converter`. Best regards, Han On Sat, Jun 12, 2021 at 2:55 PM Darafei "Komяpa" Praliaskouski < m...@komzpa.net> wrote: > Hello, > > the abbrev_converter is applied whenever it is defined. The values are > sorted using the abbreviated comparator first using the shortened version, > and if there is a tie the system asks the real full comparator to resolve > it. > > This article seems to be rather comprehensive: > https://brandur.org/sortsupport > > On Sat, Jun 12, 2021 at 9:51 AM Han Wang <hanwg...@gmail.com> wrote: > >> Hi all, >> >> I am trying to implement a sort support function for geometry data types >> in PostGIS with the new feature `SortSupport`. However, I have a question >> about this. >> >> I think it is hardly to apply a sort support function to a complex data >> type without the `abbrev_converter` to simply the data structure into a >> single `Datum`. However, I do not know how the system determines when to >> apply the converter. >> >> I appreciate any answers or suggestions. I am looking forward to hearing >> from you. >> >> Best regards, >> Han >> > > > -- > Darafei "Komяpa" Praliaskouski > OSM BY Team - http://openstreetmap.by/ >
