[Qgis-developer] Fwd: Re: [Geopackage] Geopackage on a shared network drive

[Even Rouault]

Le mercredi 05 octobre 2016 21:51:03, vous avez écrit :
> On 05-10-16 17:17, Even Rouault wrote:
> > Does such behaviour of files on network shares on Windows ring a bell to
> > someone ? I tried (quickly) to find if this was a documented behaviour
> > but didn't manage to find.
> 
> Hi Even, well this rang with me:
> 
> https://hub.qgis.org/issues/6448
> 
> it's an old discussion about reading shapefiles over a Windows network...
> 
> And it was also talking about VSI_CACHE, and I also (from the issue) had
> a little chat with Frank W about it:
> 
> http://irclogs.geoapt.com/gdal/%23gdal.2012-07-25.log
> 
> HTH maybe

Thanks for the pointers. Helpful indeed.

The situation has changed since now QGIS
opens the shapefile handle of the QgsOgrProvider object in read-only mode by
default (used to be read-write before latest 1.16 and 1.14 point releases), hence
I'm wondering if the VSI_CACHE mechanism has still some effect on the read-only handles owned
by the QgsOgrFeatureIterator objects, which are the ones that matter for rendering operations.

Seeing https://msdn.microsoft.com/en-us/library/windows/desktop/aa365433%28v=vs.85%29.aspx
which is about opportunistic locks, I would think that a read-write file handle would defeat
opportunistic locks, hence the slowness seen. That would also what Radim suggested in a comment :
"OpLocks are broken for read only files, not for read write files if opened as read only, at least this was observed on Windows XP + Samba"


-- 
Spatialys - Geospatial professional services
http://www.spatialys.com