[postgis-devel] Btree operators

[Paul Ramsey]

Speed is a benefit. Once you start down the road of = semantics, the
question of "which equals" looms large. Spatial equality?
Representational equality? Equality within a tolerance? Doing a string
compare is basically the only one that doesn't impose a surprising
cost, and it is, as you say, noisy.

WRT ordering, I did actually briefly have a z-ordering approach in
place, but I cannot remember why I had to drop it: but I did. Shame
about my memory on that.

P

On Thu, Apr 7, 2016 at 6:22 AM, Daniel Baston <dbaston at gmail.com> wrote:
> I've seen plenty of users (including myself) confused by the = operator,
> especially when it's implicitly accessed in cases like DISTINCT, DISTINCT
> ON(), and GROUP BY.  The workaround, to serialize and do a string compare,
> can really add a lot of noise to a query.  Are there benefits that come from
> the current behavior of the = operator, besides the (high) value of
> backwards compatibility?
>
> Dan
>
> On Thu, Apr 7, 2016 at 7:22 AM, Komяpa <me at komzpa.net> wrote:
>>
>> hey there,
>>
>> https://trac.osgeo.org/postgis/ticket/3521 floated nearby me and broke my
>> heart.
>>
>> Can we have SELECT DISTINCT work for sure as a complete compare, not just
>> bbox one?
>>
>> It also touches the topic of sorting the boxes - it seems now they're
>> sorted by X, then by Y - which is usually a poor way to preserve spatial
>> locality. Can we sort by z-order curve instead? just bit-mix all the
>> coordinates: https://en.wikipedia.org/wiki/Z-order_curve - that will make
>> painful voodoo stuff like ORDER BY
>> ST_GeoHash(ST_Transfrom(ST_Centroid(geom),4326)) much cleaner and replace it
>> with just CLUSTER (see https://github.com/openstreetmap/osm2pgsql/issues/208
>> ).
>>
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>
>
>
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