Timothy Hume <T.Hume@xxxxxxxxxx> writes:
> Hi,
>
> I have encountered a situation where nc_get_vara and nc_get_vars operations
> run much slower on NetCDF-4 files than they do on NetCDF-3 files.
>
> Here is an example CDL for one of my files (with irrelevant stuff removed):
>
> netcdf ecmwf_0p5deg_ocf_t2m_mars_opn {
> dimensions:
> basetime = UNLIMITED ; // (100 currently)
> forecast = 32 ;
> bounds = 2 ;
> latitude = 121 ;
> longitude = 101 ;
> variables:
>
> float temperature_2m(basetime, forecast, latitude, longitude) ;
> temperature_2m:long_name = "Air temperature 2m above the
> surface" ;
> temperature_2m:units = "K" ;
> temperature_2m:_FillValue = 9.96921e+36f ;
> temperature_2m:missing_value = 9.96921e+36f ;
> temperature_2m:valid_min = 180.f ;
> temperature_2m:valid_max = 330.f ;
> temperature_2m:standard_name = "air_temperature" ;
> temperature_2m:cell_methods = "area: mean" ;
> temperature_2m:coordinates = "level" ;
> }
>
> I can create a NetCDF-3 or NetCDF-4 file using this CDL. The problem is that
> when I try slicing out a single record (on the unlimited dimension) using
> nc_get_vara or nc_get_vars functions, it can take an order of magnitude
> (really) longer on a NetCDF-4 file than with a NetCDF-3 file. This affects
> NetCDF-4 files with or without compression. I've experimented with various
> NetCDF-4 chunking options, and that doesn't help either.
>
> Has anyone else encountered such slowness issues with NetCDF-4? My solution
> is to keep the data files in NetCDF-3, but I would really like to migrate to
> NetCDF-4.
>
Howdy Tim!
Can you try this with the latest beta release?
There have been many performance improvements since the 4.1.1 release...
Thanks,
Ed
--
Ed Hartnett -- ed@xxxxxxxxxxxxxxxx
