Bug report #8101: "Save as" on a large PostGIS point layer doesn't work - QGIS Application - QGIS Issue Tracking

Bug report #8101

"Save as" on a large PostGIS point layer doesn't work

Added by Aren Cambre almost 11 years ago. Updated about 5 years ago.

Status:	Closed
Priority:	Low
Assignee:	-
Category:	Vectors
Affected QGIS version:	master	Regression?:	No
Operating System:		Easy fix?:	No
Pull Request or Patch supplied:	No	Resolution:	end of life
Crashes QGIS or corrupts data:	No	Copied to github as #:	16936

Description

On 1.8.0 and 1.9 192e130, I load a PostGIS layer with 2,889,598 points. These represent a few years' worth of a type of event along roadways in a state of the United States. I right-click on the layer, select Save As, select a path and filename, check Skip attribute creation (the layer has a lot of attributes; don't need them in the SHP), and press OK. I don't change the Format field from ERSI Shapefile.

QGIS just hangs for a few minutes. It eventually gives the attached error. It does produce a SHP (also attached in a ZIP), but the file sizes are far too small. The DBF only has 1253 data rows.

(Just to be clear, I can't share the data due to state law and confidentiality agreements.)

save_as_error.png (28.1 KB) Aren Cambre, 2013-06-18 09:26 AM

test.zip (28.8 KB) Aren Cambre, 2013-06-18 09:26 AM

heatmap_errors.txt (46.9 KB) Aren Cambre, 2013-06-18 12:09 PM

History

#1 Updated by Giovanni Manghi almost 11 years ago

Status changed from Open to Feedback

I tested with a 568k polygon layer on a remote postgis server, and it took about 2 minutes to export it as shape (without attributes).

I will see if I can find something bigger...

#2 Updated by Aren Cambre almost 11 years ago

This is interesting. I get the same symptom if I use the Filter feature to bring the layer down to about 6000 points.

Checking on other factors...

#3 Updated by Aren Cambre almost 11 years ago

OK, on the export of the filtered subset of only about 6000 points, it takes about 6 minutes to complete. I've attached the output of the error dialog.

While this is happening, QGIS is using 100% of one of my CPUs.

Postgres has little activity, verified both through CPU usage and pgAdmin III's Server Status feature. All it does is receive occasional FETCH FORWARD 2000 FROM qgisf0 commands every minute or two, and that appears to produce 12 locks.

Something that could be distinctive is this PostGIS table has 148 columns (including the numeric index and geometry columns).

#4 Updated by Aren Cambre almost 11 years ago

File heatmap_errors.txt added

Here's that file of the heatmap errors.

#5 Updated by Aren Cambre almost 11 years ago

Interesting: I ran the same operation back to back (with the filtered dataset). It took 6 minutes the first time, 19 minutes the second time.

#6 Updated by Aren Cambre almost 11 years ago

Just tried again but without checking the Skip attribute creation box. The only real difference here was that the DBF part of the ShapeFile was huge, as expected, due to all the attributes. It still took a very long time.

#7 Updated by Aren Cambre almost 11 years ago

I have a SQL dump of the PostGIS datasource handy, so I can share it with you. Please email me at [email protected] to get it.

#8 Updated by Giovanni Manghi almost 11 years ago

Status changed from Feedback to Open
Priority changed from Normal to Low
Category changed from GUI to Vectors
Subject changed from "Save as" on large Postgres point layer doesn't work to "Save as" on large a PostGIS point layer doesn't work

This are my findings:

exporting large/huge postgis layers works ok: I tested on layers with up to 5 million features and in general it works ok (with "save as...")

I confirm that with your dataset the operation (save as...) fails after a few minutes with a list of

Feature creation error (OGR error: Pointer 'hFeat' is NULL in 'OGR_L_SetFeature'. )Stopping after 1001 errors

errors

exporting the same dataset with ogr2ogr is ok and gives the expected shapefile

exporting with pgsql2shp seems to work fine, but beside not returning any error the number of features is not the same as the original postgis layer

#9 Updated by Matthias Kuhn almost 11 years ago

There's a hardcoded limit of 1000 allowed errors in QgsVectorFileWriter (qgsvectorfilewriter.cpp:860).
This could (and should) be made configurable. But this leaves open the question of which features fail to be written and for what reason.

#10 Updated by Nathan Woodrow almost 11 years ago

Why is there a hard coded limit? That is pretty bad design IMO. We should just write what we can and report what we couldn't at the end.

#11 Updated by Giovanni Manghi almost 11 years ago

Subject changed from "Save as" on large a PostGIS point layer doesn't work to "Save as" on a large PostGIS point layer doesn't work

Matthias Kuhn wrote:

There's a hardcoded limit of 1000 allowed errors in QgsVectorFileWriter (qgsvectorfilewriter.cpp:860).
This could (and should) be made configurable. But this leaves open the question of which features fail to be written and for what reason.

as I said the operation in general works ok even for very large postgis vectors. With this particular dataset there is this problem.

#12 Updated by Aren Cambre almost 11 years ago

Is there anything unique about this dataset? I haven't noticed any problems viewing it. It's just a bunch of points.

#13 Updated by Bill Morris almost 10 years ago

I've just run into the same error on a point file with 100 features and a single attribute column. Only 86 out of 100 exported. This bug is still out there.

https://gist.github.com/wboykinm/751a02d51f95ddb3f5cd

Aren Cambre wrote: