[postgis-devel] Caching function calls with CTEs

[Paragon Corporation]

Nicklas,
 
 I can't quite see how max distance would help ST_DWithin.  It seems it
would help the Fully_DWithin, but don't see how it helps the ST_DWithin.
Granted I haven't given it much thought.  
 
Thanks,
Regina

  _____  

From: postgis-devel-bounces at postgis.refractions.net
[mailto:postgis-devel-bounces at postgis.refractions.net] On Behalf Of
nicklas.aven at jordogskog.no
Sent: Sunday, July 19, 2009 2:39 PM
To: PostGIS Development Discussion
Subject: Re: [postgis-devel] Caching function calls with CTEs


Yes,that one I can see.

About the nearest neighbour I have thought about using st_max_distance
against the bounding boxes to find the one with smallest max_distance. That
value ought to be good to use in the st_dwithin part of the query. 

Maybe it would even be worth the effort to use st_distance from the geometry
found with the "max_distance" boundingbox to usi in in st_dwithin. 

Hope it is possible to understand what I mean. It is at least one release
ahead but possible to test :-)


/Nicklas





				

2009-07-19 Paragon Corporation wrote:

> 
Windowing functions come in especially handy for nearest neighbor search
getting top n per location.  We are going to demonstrate that in our OSCON
conference.  Slides and materials will of course will be available after the
conference is over.

>> 
  _____  

From: postgis-devel-bounces at postgis.refractions.net
[mailto:postgis-devel-bounces at postgis.refractions.net] On Behalf Of
nicklas.aven at jordogskog.no
>Sent: Sunday, July 19, 2009 1:52 PM
>To: PostGIS Development Discussion
>Subject: Re: [postgis-devel] Caching function calls with CTEs
>
>
> 
 
This is really cool Regina and Leo
>
>It's a new way of thinking for me to to use this recursive thing, but I can
see that it is very useful.
>I hope I will get some time in the near future to try to understand it
better.
>
>Also the windowing functions together with postgis aggregate function will
be fun to try.
>
>/Nicklas
>
>
>
>
>
>2009-07-17 Paragon Corporation wrote:
>
>Nicklas,
>>
>>We tried CTEs against that annoying issue of functions not being cached in
>>the same row. Preliminary tests seem to suggest it might be the ideal
>>solution for this.
>>We suspect it will also be good in many other scenarios where the planner
>>refuses to use indexes in the right order etc.
>>
>>http://www.postgresonline.com/journal/index.php?/archives/127-guid.html
>>
>>We are going to test with real spatial queries next in preparation for our
>>OSCON presentation next week.
>>
>>http://en.oreilly.com/oscon2009/public/schedule/detail/7859
>>Sadly it looks like we probably won't have 1.4 out in time for our
>>presentation - oh well :(
>>
>>
>>Anyrate take a look and test with your data to see if it speeds up your
>>queries.
>>
>>L & R
>>
>>
>>_______________________________________________
>>postgis-devel mailing list
>>postgis-devel at postgis.refractions.net
>>http://postgis.refractions.net/mailman/listinfo/postgis-devel
>>
>> 
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