[postgis-devel] Wobbles

[Paul Ramsey]

Yeah, looks like it wobbles. Two runs, no change in anything at all, just two SQL statements one after another

postgis=# select sum(st_area(geom::geography)) from va;
        sum         
--------------------
 1070124793748.3967
(1 row)

Time: 1345.384 ms (00:01.345)
postgis=# select sum(st_area(geom::geography)) from va;
        sum         
--------------------
 1070124793748.3954
(1 row)

Time: 1352.277 ms (00:01.352)



> On Apr 28, 2021, at 1:34 PM, Regina Obe <lr at pcorp.us> wrote:
> 
> I know the difference is pretty small, but how did you manage to get two
> different answers for area with just swap of GEOS or is that a typo?
> 
> In 3.8.3 you have  1070124793748.3967
> 
> In 3.9.2dev you have 1070124793748.3959
> 
> Is that 2 digit different just voodoo powder.
> I thought given  the same exact machine, same version of PostGIS  and same
> version of Proj we could count on no randomness of answers.
> 
> Is the answer the same each and every time you run it for a given setup or
> does it wabble a bit?
> 
>> -----Original Message-----
>> From: postgis-devel [mailto:postgis-devel-bounces at lists.osgeo.org] On
>> Behalf Of Paul Ramsey
>> Sent: Tuesday, April 27, 2021 4:47 PM
>> To: PostGIS Development Discussion <postgis-devel at lists.osgeo.org>
>> Subject: Re: [postgis-devel] Much slower processing on GEOS 3.9.0 versus
>> 3.8.0 for geodesic area calculation
>> 
>> Just to stick a nail in the GEOS-version-affects-geography-area
> conversation,
>> I took the time to set up two builds (GEOS 3.8 and GEOS 3.9) and swapped
>> between them without changing anything else about the system.
>> 
>> postgis=# select postgis_full_version();
>> 
>> postgis_full_version
>> 
> ----------------------------------------------------------------------------
> ------------------
>> 
> ----------------------------------------------------------------------------
> ------------------
>> 
> ----------------------------------------------------------------------------
> ------------------
>> 
> ----------------------------------------------------------------------------
> ---
>> POSTGIS="3.2.0dev 3.1.0rc1-162-g46efb9f2d" [EXTENSION] PGSQL="130"
>> GEOS="3.8.3-CAPI-1.13.4" PROJ="8.0.0" GDAL="GDAL 3.2.0, released
>> 2020/10/26" LIBXML="2.9.4" LIBJSON="0.15" LIBPROTOBUF="1.3.3"
>> WAGYU="0.5.0 (Internal)"
>> 
>> postgis=# select sum(st_area(geom::geography)) from va;
>>        sum
>> --------------------
>> 1070124793748.3967
>> (1 row)
>> 
>> Time: 1449.551 ms (00:01.450)
>> 
>> 
>> Then stop the server, change the LD_LIBRARY_PATH to the 3.9 install
> location
>> and restart.
>> 
>> postgis=# select postgis_full_version();
>> 
>> postgis_full_version
>> 
> ----------------------------------------------------------------------------
> ------------------
>> 
> ----------------------------------------------------------------------------
> ------------------
>> 
> ----------------------------------------------------------------------------
> ------------------
>> 
> ----------------------------------------------------------------------------
> ------
>> POSTGIS="3.2.0dev 3.1.0rc1-162-g46efb9f2d" [EXTENSION] PGSQL="130"
>> GEOS="3.9.2dev-CAPI-1.14.2" PROJ="8.0.0" GDAL="GDAL 3.2.0, released
>> 2020/10/26" LIBXML="2.9.4" LIBJSON="0.15" LIBPROTOBUF="1.3.3"
>> WAGYU="0.5.0 (Internal)"
>> 
>> postgis=# select sum(st_area(geom::geography)) from va;
>>        sum
>> --------------------
>> 1070124793748.3959
>> (1 row)
>> 
>> Time: 1439.969 ms (00:01.440)
>> 
>> 
>> 
>> There's no effect to be seen when GEOS version is the only variable in
> play.
>> 
>> P
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> 
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