[postgis-devel] Another Data Point

[Martin Davis]

Could be...   It would be interesting to see whether GEOS is faster than 
JTS.   Needs a test environment able to run both pieces of code on the 
same hardware.

Paul Ramsey wrote:
> I got another run in, right near the end, and it showed that
> GEOSUnionCascaded took only about 50% of the time in that slice. There
> was still more memcpy'ing first. I bet GEOSUnionCascaded on its own
> would be as fast as JTS (or faster?).
>
> P.
>
> On Wed, Jan 21, 2009 at 9:05 AM, Paul Ramsey <pramsey at cleverelephant.ca> wrote:
>   
>> Interesting! The Shark only samples for about 20 seconds, so I only
>> got the first 10% or so of the run, and the biggest user in that time
>> period memcpy'ing in LWGEOM_accum (postgis) and
>> advance_transition_function (pgsql). So we are spending a non-trivial
>> amount of time just accumulating the input...
>>
>> P
>>
>> On Wed, Jan 21, 2009 at 9:00 AM, Paul Ramsey <pramsey at cleverelephant.ca> wrote:
>>     
>>> The glove is dropped indeed... why speculate when I have the Shark...
>>> time to see where our time goes...
>>>
>>> P
>>>
>>> On Wed, Jan 21, 2009 at 8:55 AM, Martin Davis <mbdavis at refractions.net> wrote:
>>>       
>>>> Go for it, Regina!  The glove is dropped...
>>>>
>>>> Although I suspect this test may simply be running into the slower memory
>>>> performance due to any or all of Postgres, C, GEOS compared to good ol'
>>>> Java...  Hard to beat that tuned JVM memory manager!
>>>>
>>>> Obe, Regina wrote:
>>>>         
>>>>> Ah I think JTS was able to do this in about 40-50 seconds.  And my
>>>>> version was able to beat out Kevin's nested by a small margin.  I'll
>>>>> retest on mine.
>>>>>
>>>>> So I think we still need work here.
>>>>>
>>>>> I'm curious what would happen if I combined the algorithm I wrote with
>>>>> the new ST_Union how things would fair.  In theory it should fair the
>>>>> same, but I'm not really using Martin's cascaded union algorithm to the
>>>>> letter.
>>>>>
>>>>>
>>>>> -----Original Message-----
>>>>> From: postgis-devel-bounces at postgis.refractions.net
>>>>> [mailto:postgis-devel-bounces at postgis.refractions.net] On Behalf Of Paul
>>>>> Ramsey
>>>>> Sent: Wednesday, January 21, 2009 12:50 AM
>>>>> To: PostGIS Development Discussion
>>>>> Cc: lee.keel at uai.com
>>>>> Subject: [postgis-devel] Another Data Point
>>>>>
>>>>> Using the original sample set from Lee Keel,
>>>>>
>>>>> With the old style ST_Union, 3 hours, 27 minutes:
>>>>>
>>>>> uniontest=# select st_area(st_union(the_geom)) from sample_poly;
>>>>>      st_area
>>>>> --------------------
>>>>>  0.0324039850011104
>>>>> (1 row)
>>>>>
>>>>> Time: 12419261.819 ms
>>>>>
>>>>>
>>>>> With the new cascaded ST_Union, 4 minutes, 30 seconds, or 46 times
>>>>> faster.
>>>>>
>>>>> uniontest=# select st_area(st_union_fast(the_geom)) from sample_poly;
>>>>>      st_area
>>>>> --------------------
>>>>>  0.0324039850054305
>>>>> (1 row)
>>>>>
>>>>> Time: 271618.181 ms
>>>>>
>>>>>
>>>>> That's one nasty data set.
>>>>>
>>>>> P.
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>>>>>
>>>>>           
>>>> --
>>>> Martin Davis
>>>> Senior Technical Architect
>>>> Refractions Research, Inc.
>>>> (250) 383-3022
>>>>
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>>>>
>>>>         
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>   

-- 
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022