Hi Ed,
Seems reasonable. (We _really_ need to increase the default chunk cache
size... :-)
Quincey
> Howdy all!
>
> Based on recent emails and discussions, here's an attempt at
> requirements relating to the setting of chunksizes. This is from the
> requirements at
> http://my.unidata.ucar.edu/content/software/netcdf/netcdf-4/reqs.html.
>
> * Chunking is required in any dataset with one or more unlimited
> dimension in HDF5. NetCDF-4 supports setting chunk parameters at
> variable creation with the following new function:
>
> int nc_def_var_x(int ncid, const char *name, nc_type xtype, int ndims,
> const int *dimidsp, int *varidp, int chunkalg, int *chunksizes);
>
> Where chunksize is a pointer to an array of size ndims, with the
> chunksize in each dimension. If chunksizes is NULL, the user can
> select a chunking algorithm by setting chunkalg to NC_CHUNK_SEQ
> (to optimize for sequential access), NC_CHUNK_SUB (for chunk
> sizes set to favor equally subsetting in any dimension.
>
> When the (netcdf-3) function nc_def_var is used, a sequential
> chunking algorithm will be used. (Just as if the var had been
> created with NC_CHUNK_SEQ).
>
> The sequential chunking algorithm sets a chunksize of 1 all
> unlimited dimensions, and all other chunksizes to the size of
> that dimension, unless the resulting chunksize is greater than
> 250 KB, in which case subsequent dimensions will be set to 1
> until the chunksize is less than 250 KB (one quarter of the
> default chunk cache size).
>
> The subsetting chunking algorithm sets the chunksize in each
> dimension to the nth root of (desired chunksize/product of n
> dimsizes).
>
>
