On 12/15/2014 08:32 PM, Alexander Korotkov wrote:
On Mon, Dec 15, 2014 at 7:47 PM, Heikki Linnakangas <hlinnakan...@vmware.com
wrote:
On 12/15/2014 05:22 PM, Alexander Korotkov wrote:
On Mon, Dec 15, 2014 at 6:20 PM, Tom Lane <t...@sss.pgh.pa.us> wrote:
Alexander Korotkov <aekorot...@gmail.com> writes:
On Mon, Dec 15, 2014 at 4:12 PM, Heikki Linnakangas <
hlinnakan...@vmware.com
wrote:
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.
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:
[ query using ORDER BY ST_Distance ]
It's not apparent to me that the proposed operator is a replacement for
ST_Distance. The underlying data in an example like this won't be either
points or polygons, it'll be PostGIS datatypes.
In short, I believe that PostGIS could use what you're talking about,
but I agree with Heikki's objection that nobody has asked for this
particular operator.
"polygon <-> point" is for sure not ST_Distance replacement. I was giving
this argument about KNN-GiST with recheck itself. "polygon <-> point" is
needed just as in-core example of KNN-GiST with recheck.
Right. I don't think point <-> polygon is too useful by itself, but we
need an example in core that could make use KNN-GiST recheck patch. We
can't write a regression test for it otherwise, for starters.
Actually, we probably could've used the circle <-> polygon for that just
as well...
Did you mean searching for circles or polygons in the last sentence?
circle as the key, on an index on a polygon column. A circle with radius
0 is equivalent to a point, after all.
I'm looking at the knn-gist with recheck patch now, and I see that it
actually adds two more operators: polygon <-> point (commutator of what
I just committed) and circle <-> point. We might want to split those off
into a separate patch too.
- Heikki
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