[postgis-devel] CascadedUnion Early Results

Obe, Regina robe.dnd at cityofboston.gov
Tue Jan 20 13:42:35 PST 2009


Paul, 

I think we can do better. 

As I recall with my cascade union tests I was getting comparable speed
and JTS was about 2-10 times faster.


Can you test the attached data set out.  Then it will be a closer
comparison.  I think for this set JTS was about 20 seconds.

Below is the link to my results on this way back.

http://postgis.refractions.net/support/wiki/index.php?PL%2FPGSQL%20Pseud
o%20Cascade%20Union%20Aggregate%20Function


(though I don't have the JTS one listed there)

Damn I hope this is the right dataset.  I'll retest on my other box but
I have so many of these lying around.

Would also be interesting to repeat Kevin's original test that started
this all out.  I can send you that dataset off list.

Thanks,
Regina




-----Original Message-----
From: postgis-devel-bounces at postgis.refractions.net
[mailto:postgis-devel-bounces at postgis.refractions.net] On Behalf Of Mark
Cave-Ayland
Sent: Tuesday, January 20, 2009 4:34 PM
To: PostGIS Development Discussion
Subject: Re: [postgis-devel] CascadedUnion Early Results

Paul Ramsey wrote:

> For completeness, the whole table, about 4x faster:
> 
> uniontest=# select count(*) from counties;
>  count
> -------
>   3140
> (1 row)
> 
> uniontest=# select st_area(st_union(the_geom)) from counties;
st_area
> ------------------
>  1095.88034519544
> (1 row)
> 
> Time: 42352.399 ms
> 
> uniontest=# select st_area(st_union_fast(the_geom)) from counties;
>      st_area
> ------------------
>  1095.88034519544
> (1 row)
> 
> Time: 11493.832 ms

Fascinating. What would be really interesting would be to compare the 
times with the same dataset in JTS so we can get a feel as to whether 
there is any more overhead in the array_accum/GEOS conversion code.


ATB,

Mark.

-- 
Mark Cave-Ayland
Sirius Corporation - The Open Source Experts
http://www.siriusit.co.uk
T: +44 870 608 0063
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