[gdal-dev] Slow GDALComputeRasterMinMax on nc grids
jmckenna at gatewaygeomatics.com
Fri Jan 3 12:03:47 PST 2020
On 2020-01-03 3:52 PM, Even Rouault wrote:
> Do you build netCDF with a custom value of the CHUNK_CACHE_SIZE / chunk-cache-
> size setting ?
> With the default (4 MB), runtime on my machine is about 7 minutes. But if I
> use --with-chunk-cache-size=67108864 as in
> https://trac.osgeo.org/gdal/ticket/5291#comment:26 , then it goes down to
> 9 sec.
> So this is a quite old known issue with the netCDF driver with HDF5 chunking &
> compression. Due to the netCDF driver exposing rasters with a north origin,
> and netCDF Y origin being at south, there's a mismatch between GDAL blocks and
> netCDF chunks. So for the sake of simplicity, the netCDF driver exposes one
> single line as the GDAL block size. It could/should be improved to make a
> better use of netCDF chunks, so as not being too much dependent of the quite
> pessimistic default of the netCDF chunk_cache_size.
No I don't set CHUNK_CACHE_SIZE during compile at all. I do however set
(I believe I set that because of that same chunking issue which we
discussed here before)
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