[gdal-dev] Slow GDALComputeRasterMinMax on nc grids

[Jeff McKenna]

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.
> 

Hi Even,

No I don't set CHUNK_CACHE_SIZE during compile at all.  I do however set 
USE_HDF5=OFF

(I believe I set that because of that same chunking issue which we 
discussed here before)

-jeff





-- 
Jeff McKenna
MapServer Consulting and Training Services
https://gatewaygeomatics.com/