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 <[email protected]> On Behalf Of Jeff McKenna
Sent: Friday, January 3, 2020 8:04 PM
To: [email protected]
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
MapServer Consulting and Training Services https://gatewaygeomatics.com/
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