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

[Nicolas Cadieux]

Hi, 
The Qgis dissolve is very slow. I tried to dissolve a SRTM water layer for province of Quebec and was unable to do it even with 64GB of memory and a SSD and 6 or 7 days of processing.    Use the Saga (or Grass) dissolve found in the processing toolbar.  It can do it in minutes! 
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 1:58 PM, "Alex Mandel-2 [via OSGeo.org]" <ml-node+s1560n5221843h94 at n6.nabble.com> wrote: 

	Kenneth,
How many records, and how much memory do the files take on disc?
Are you joining the SHP and the CSV and then doing Dissolve? Did you
save the joined layer to a new file? Does this shapefile have a spatial
index created? Is the topology of the polygons clean (are there self
intersections, lots of slivers, or overlaps?
Other than saving the intermediate to a file, the next suggestion is to
use Spatialite or Postgis databases.
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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