Re: Commit fest 2014-12, let's begin!

On Mon, Dec 15, 2014 at 4:12 PM, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com
> wrote:
>
> On 12/15/2014 08:37 AM, Michael Paquier wrote:
>
>> On Mon, Dec 15, 2014 at 3:09 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>
>>> Michael Paquier <michael(dot)paquier(at)gmail(dot)com> writes:
>>>
>>>> - Point to polygon distance operator
>>>>
>>> I looked at that briefly during the last fest, but was unsure whether it
>>> was too entangled with the GiST patches that Heikki was looking at.
>>>
>> Recalling my memories of this morning, things are rather independent.
>>
>
> Right. I also looked at it briefly, but I wasn't sure if we really want
> it. AFAICT, no-one has actually asked for that operator, it was written
> only to be an example of an operator that would benefit from the knn-gist
> with recheck patch. If there is some other, real, use for the knn-gist with
> recheck patch, then I'm OK with that, but otherwise it's dubious to add an
> operator just so that it can then be made faster by another patch. That
> said, it seems quite harmless, so might as well commit it.

Lack of recheck is major limitation of KNN-GiST now. People are not asking
for that because they don't know what is needed to implement exact KNN for
PostGIS. Now they have to invent kluges like this:

WITH closest_candidates AS (
SELECT
streets.gid,
streets.name,
streets.geom
FROM
nyc_streets streets
ORDER BY
streets.geom <->
'SRID=26918;POINT(583571.905921312 4506714.34119218)'::geometry
LIMIT 100
)
SELECT gid, name
FROM closest_candidates
ORDER BY
ST_Distance(
geom,
'SRID=26918;POINT(583571.905921312 4506714.34119218)'::geometry
)
LIMIT 1;

See blog posts:
http://blog.light42.com/wordpress/?p=102
http://workshops.boundlessgeo.com/postgis-intro/knn.html

------
With best regards,
Alexander Korotkov.