[gdal-dev] Slow GDALComputeRasterMinMax on nc grids

[Joaquim Manuel Freire Luís]

But I do use

		-DCHUNK_CACHE_SIZE=67108864 ^
		-DDEFAULT_CHUNK_SIZE=67108864

And get ~6 sec with a GMT release build (before it was a debug build) but still ~27 sec with gdalinfo. All VS2019 builds

-----Original Message-----
From: gdal-dev <gdal-dev-bounces at lists.osgeo.org> On Behalf Of Jeff McKenna
Sent: Friday, January 3, 2020 8:04 PM
To: gdal-dev at lists.osgeo.org
Subject: Re: [gdal-dev] Slow GDALComputeRasterMinMax on nc grids

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
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