[Qgis-user] Incredibly slow performance using QGIS v2.10

Sun Aug 30 23:59:06 PDT 2015

Hi all,

I have a pull request pending [1] that tremendously speeds up QGIS' own 
dissolve if using a dissolve field.
I got an error when using GRASS' dissolve in a model.

Bernhard

[1] https://github.com/qgis/QGIS/pull/2263/files

Am 31.08.2015 um 01:34 schrieb Alex Mandel:
> I agree try Nicolas' suggestions first as they are easiest.
>
> My suggestion of Spatialite or Postgis was to also move the dissolve
> into a different tool as you would use the Dissolve function inside
> those DB formats with a query.
> SELECT stuff, dissolve(geom)
> FROM layer
> GROUP BY yourdissolvecolumn
>
>
> Thanks,
> Alex
>
> On 08/30/2015 02:42 PM, Nicolas Cadieux wrote:
>> Hi,
>> I suggest to take the joined saved .shp file and use the Saga version of dissolve.  Using the Spatialite (click on layer and save shp as Spatialite) file could make things faster but the problem here is, to my knowledge, not the file format.  It's the QGIS dissolve.  See below.
>> http://gis.stackexchange.com/questions/79850/merge-large-number-of-polygons-using-qgis
>> Saga (processing plugin) will ask for a field for this dissolve.  Select the zip field or create a new Field with a dummy variable if you want to dissolve all.  (Use the field calculator if you which to  create this dummy variable).  If you see slivers, you can set a tolerance level (unit will be the unit of your CRS).
>> Good luck!
>> Nicolas Cadieux M.Sc.
>> Les Entreprises Archéotec inc. 
>> 8548, rue Saint-Denis Montréal H2P 2H2
>> Téléphone: 514.381.5112  Fax: 514.381.4995
>> www.archeotec.ca
>> On Aug 30, 2015 16:47, "Ken Walenga [via OSGeo.org]" <ml-node+s1560n5221860h21 at n6.nabble.com> wrote:
>>
>> 	I have replied to your questions in-line, below: On Sun, Aug 30, 2015 at 11:03 AM, Alex Mandel < [hidden email] > wrote: <blockquote style="border-left:2px solid #cccccc;padding:0 1em" style="margin:0 0 0 0.8ex;border-left:1px #ccc solid;padding-left:1ex">Kenneth,
>>
>> How many records, and how much memory do the files take on disc? The Zip.shp file contains 41,342 rows and takes up ca. 400KB on disk. The Zip2Terr.csv file contains 87,632 rows and occupies 4KB on disk. <blockquote style="border-left:2px solid #cccccc;padding:0 1em" style="margin:0 0 0 0.8ex;border-left:1px #ccc solid;padding-left:1ex">
>>
>> Are you joining the SHP and the CSV and then doing Dissolve? Yes. <blockquote style="border-left:2px solid #cccccc;padding:0 1em" style="margin:0 0 0 0.8ex;border-left:1px #ccc solid;padding-left:1ex"> Did you
>> save the joined layer to a new file? Yes <blockquote style="border-left:2px solid #cccccc;padding:0 1em" style="margin:0 0 0 0.8ex;border-left:1px #ccc solid;padding-left:1ex">Does this shapefile have a spatial
>> index created? Yes <blockquote style="border-left:2px solid #cccccc;padding:0 1em" style="margin:0 0 0 0.8ex;border-left:1px #ccc solid;padding-left:1ex"> Is the topology of the polygons clean (are there self
>> intersections, lots of slivers, or overlaps? It is clean. There don't appear to be any slivers. <blockquote style="border-left:2px solid #cccccc;padding:0 1em" style="margin:0 0 0 0.8ex;border-left:1px #ccc solid;padding-left:1ex">
>>
>> Other than saving the intermediate to a file, the next suggestion is to
>> use Spatialite or Postgis databases. Can you elaborate a little on what's involved in using one of the two named databases? Do I simply need to read the .csv file into Spatiallite or Postgres? <blockquote style="border-left:2px solid #cccccc;padding:0 1em" style="margin:0 0 0 0.8ex;border-left:1px #ccc solid;padding-left:1ex">
>>
>> Keep in mind, that an operation like this is single threaded.
>>
>> Thanks,
>> Alex
>>
>> On 08/30/2015 09:53 AM, Ken Walenga wrote:
>> > Looking for help. I have an unsimplified ZIP.shp file and want to create my
>> > own custom boundary files for territories which are a collection of zip
>> > code areas. I bring in the Zip.shp file and  join to a Zip2Terr.csv file on
>> > the Zip field. When I try to dissolve the TERR_NBR field, the dissolve
>> > process can take longer than 2 whole days (!). Any ideas on ways to speed
>> > it up? I have tried using a simplified Zip.shp file, but that results in
>> > way less than satisfactory boundary files with gaps, etc. Might this be a
>> > problem with v2.10? Is it possible that I would see better performance
>> > using an earlier rev?
>> >
>> > I am using v2.10 of QGIS, running on a Win7 HP destop machine, quad core, 8
>> > GB RAM.
>> >
>> > Thanks.
>> >
>> > ----
>> > Kenneth Walenga
>> > Commercial BI & Reporting
>> > Genentech, A Member of the Roche Group
>> > US CommOps - USMA Data Services
>> > "Every moment matters.  Making IT happen."
>> > (O) 650-467-6855
>> > (F) 650-467-2570
>> > (M) 650-438-4505
>> >
>> >
>> >
>> > _______________________________________________
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>> >
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