[gdal-dev] New RFC - Fast Open - for discussion

[Even Rouault]

Hi

Although I agree that the goal of fast opening is a good idea, as discussed on 
IRC, I'm not sure we need this RFC for the current work plan it contains :
* listing the files in the directory can already be skipped by defining 
GDAL_DISABLE_READDIR_ON_OPEN=YES. But perhaps this could benefit from the 
mechanism of thread local configuration option
* for the GeoTIFF driver, I think the code could be reworked so that 
collecting the coordinate system is done only when GetProjectionRef() is 
called. The .aux.xml file could be opened only when GetProjectionRef(), 
GetGeoTransform() or GetMetadata() are called. 
* since GDAL 1.6.0, the GDAL VRT driver can avoid opening the underlying 
datasets if the SourceProperties elements is defined for each SimpleSource. 
This is done by the gdalbuildvrt driver. So, opening a VRT dataset should be 
really quick. The underlying datasets are opened only when real data must be 
read from them.

Currently, one area where we cannot differ the processing is the instanciation 
of raster bands. The GetRasterBand() method in GDALDataset is not virtual, so 
they must be instanciated at the dataset opening. But this is probably only 
an issue for datasets with millions of bands.

Best regards,

Even

Le Wednesday 22 April 2009 21:30:58 Frank Warmerdam, vous avez écrit :
> Folks,
>
> I have drafted a preliminary version of a new RFC for discussion.
>
>    http://trac.osgeo.org/gdal/wiki/rfc25_fast_open
>
> Feedback is welcome.
>
> Best regards,