[gdal-dev] Problems with MySQL queries in GDAL

[Even Rouault]

Pavol,

I think I have noticed that behaviour with a QGIS version of some time ago , 
and it is (was? if it is fixed now) an issue specific to QGIS that opened&closed 
many connections to GDAL when browsing through a table (and that with any GDAL 
datasource, not specifically MySQL). The logs you show are typical of this. 
Nothing that GDAL can do about (well, it could lazily establish the schema of 
the accessed layers, but that would be a micro optimization, whereas the real 
fix is to be done in QGIS). So check with QGIS folks.

Even

> Dear GDAL-developers,
> 
> I have noticed that the GDAL-Versions 1.11.2 used in QGIS 2.8 produce
> complicated queries passed to MySQL that cause huge delays in QGIS when
> working with spatial layers based on MySQL. It looks to me that GDAL
> queries each time all tables in a database, even if only a single table
> is requested. The older version 1.9.2 (used in QGIS 1.8) has not this
> issue. I have described the problem in depth here:
> 
> http://gis.stackexchange.com/questions/135865/why-are-mysql-connections-ext
> remely-slow-in-qgis-2-0-2-8-when-compared-to-qgi
> 
> The query logs of MySQL-Server can be seen here:
> https://drive.google.com/folderview?id=0B1VM28puP8EPfmF2dGpjamVDWVZ6Vm1veHg
> tOElhY2lHb0ZTSlI1WXNuWWFvU3pRQmVLMTA&usp=sharing
> 
> Can someone have a look at it? I would greatly appreciate an explanation
> of this GDAL behaviour and even more some fix or work-around. Can
> someone replicate the problem or is there something specific about my
> database design?
> 
> With best wishes,
> Pavol
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