[gdal-dev] vrt and too many open files error

[Even Rouault]

On vendredi 6 octobre 2017 17:29:40 CEST Julien Michel wrote:
> Dear all,
> 
> I have a VRT file, which I generated by a script I wrote, that simply
> mosaics 2750 tiles (images of the same size). I can not read back this
> vrt file with gdal, it says:
> 
> $ gdalinfo cloud_plain.vrt
> 
> ERROR 4: Too many open files
> gdalinfo failed - unable to open 'cloud_plain.vrt'.
> 
> Reading this tracker [1], I think it should not complain ? Note that
> this happens when parsing the vrt file, not actually reading data. If I
> gdal_translate only a small portion spanning a few tiles, it will still
> complain. Shall I file a bug report or is this behavior expected ?

Julien,

it is likely that if you built it at hand that your VRT sources lack a SourceProperties element

      <SourceProperties RasterXSize="xxx" RasterYSize="xxx" DataType="xxx" 
BlockXSize="xxx" BlockYSize="xxx" />

Without that element, GDAL must open each file, and you hit the 1024 file descriptor limit

~~~

That said, in theory the VRT driver could be improved to avoid having that element at all (and 
it would be desirable not having it). It is just needed so we can instanciate a ProxyDataset 
object since it needs to know those characteristics, but the VRT logic itself shouldn't need 
them until it identifies that it must read from the source. At the time where I improved that 
point in GDAL, I was still a bit unfamiliar with the code base and didn't dare touching that 
aspect ;-)


Even


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