[Qgis-developer] Problem with the MySQL/GDAL implementation in QGIS

[Jürgen E. Fischer]

Hi Pavol,

On Sat, 09. May 2015 at 16:58:59 +0200, Pavol Hnila wrote:
> > PostgreSQL-Users probably don't use OGR to access the database - same for
> > SpatiaLite, Oracle or MSSQL users.

> Right - there are no problems when connecting with the native QGIS provider
> for PostgreSQL. What are the chances that MySQL also gets native QGIS support
> that bypasses OGR?

From my experience MySQL is rarely used for GIS - so the demand for a mysql
provider is very low.


> > QGIS does multithreaded rendering and because OGR layers are not
> > thread safe the OGR provider always reopens the layer on every
> > rendering run.  Apparently that's not too expensive for file based
> > data sources, which I think the OGR provider is mostly used for.

> The described OGR problem emerged with QGIS 2.0. Was that version
> already influenced with multithreaded rendering?

No. MTR was introduced in 2.4.


> Anyway, it is not only that the OGR provider reopens the layer on every
> rendering run.  It is instructed by QGIS to reopen SEPARATELY every record of
> that layer and query it with all tables in the database on every rendering
> run.

That's odd.  QGIS just opens the OGR data source and the requested layer.  Does
536135a help?  It limits the data source opened for each layer to the table
it's going to request.


Jürgen

-- 
Jürgen E. Fischer           norBIT GmbH             Tel. +49-4931-918175-31
Dipl.-Inf. (FH)             Rheinstraße 13          Fax. +49-4931-918175-50
Software Engineer           D-26506 Norden             http://www.norbit.de
QGIS release manager (PSC)  Germany                    IRC: jef on FreeNode                         
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 827 bytes
Desc: Digital signature
URL: <http://lists.osgeo.org/pipermail/qgis-developer/attachments/20150509/8891a4e2/attachment.pgp>