Bug report #21839: QgsDataSourceUri parameter checkPrimaryKeyUnicity is ignored for postgres provider - QGIS Application - QGIS Issue Tracking

Bug report #21839

QgsDataSourceUri parameter checkPrimaryKeyUnicity is ignored for postgres provider

Added by Tom Vanzieleghem over 5 years ago. Updated over 5 years ago.

Status:	Closed
Priority:	Normal
Assignee:	Alessandro Pasotti
Category:	Data Provider/PostGIS
Affected QGIS version:	3.7(master)	Regression?:	No
Operating System:		Easy fix?:	No
Pull Request or Patch supplied:	Yes	Resolution:	fixed/implemented
Crashes QGIS or corrupts data:	No	Copied to github as #:	29654

Description

Initial loading time of large PostgreSQL views (> 10 million records) seems to have increased considerably compared to QGis 2. After observing the db logs I noticed the sql queries for checking primary key unicity is one of the causes for this. From the API documentation I had the impression that this behaviour could be disabled by setting the property TrustLayerMetadata on the project to true (in the GUI under project properties). This did not make a difference when loading new PG layers.

So I tried setting the parameter checkPrimaryKeyUnicity to '0' in several ways (editing an exported layer definition file and through pyqgis) but it did not make a difference.
Seems that, in case of a postgres provider, the parameter checkPrimaryKeyUnicity set on the QgsDatasourecUri instance is changed depending on the layerOptions (more specific the readExtentFromXml option) specified on the QgsVectorLayer class. The parameter also seems to disappear in the uri string after loading into the canvas and/or saving as a layer definition file.

I always was impressed with the loading of postgis layers in QGis 2 but this has considerably changed in QGis 3. Is it posssible to include an option in the GUI somewhere to prevent the checks on primaryKeyUnicity or resolve this in another way?

best regards and keep up the good work,

Tom

Associated revisions

Revision 38c91e4e
Added by Alessandro Pasotti over 5 years ago

[postgres] Fix checkPrimaryKeyUnicity option

This provider option was linked to the project level option
"Trust layer metadata..." which was implemented
to speed up loading of large dataset by trusting extent
read from metadata to avoid costly operations to determine
the layer extent.

Check PK unicity on the other hand has only effect on views
and query layers and it is useful as an independent
option to prevent loading of layers that have no PK (or the
wrong one).

But the operation of determine unicity of a values in a column
can also be costly, so better to get control back to the user.

Legacy default is preserved (the project-level "Trust..." option).

Fixes #21839

Funded by RAAB.nl

Revision 4009b2d4
Added by Alessandro Pasotti over 5 years ago

[postgres] Fix checkPrimaryKeyUnicity option

Check PK unicity on the other hand has only effect on views
and query layers and it is useful as an independent
option to prevent loading of layers that have no PK (or the
wrong one).

But the operation of determine unicity of a values in a column
can also be costly, so better to get control back to the user.

Legacy default is preserved (the project-level "Trust..." option).

Fixes #21839

Funded by RAAB.nl

History

#1 Updated by Giovanni Manghi over 5 years ago

Easy fix? changed from Yes to No

Interesting... if this will not get traction I suggest you to raise the matter in the developers mailing list. Thanks!

#2 Updated by Regis Haubourg over 5 years ago

This did not make a difference when loading new PG layers

Giovanni Manghi wrote:

Interesting... if this will not get traction I suggest you to raise the matter in the developers mailing list. Thanks!

Hi, "trust" option is only acting when loading a project file I think. The use case was to speed up opening big project with data having no metadata, either in desktop or in server context.

#3 Updated by Regis Haubourg over 5 years ago

And in I confirm that whatever the "select at id" value you set, QGIS will still throw a `select count(distinct(..` query to check unicity.

I have no idea why this could be slower in QGIS3 for huge tables though.

The proposal to add a column with a checkbox "don't check unicity on load" would be the way to go. however this PostgreSQL connection dialog is already overcrowded, and very few users understand the use of "select at id" option. I think we should work on tooltips and UI design here.