netCDF  4.3.0
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The Chunk Cache

When data are first read or written to a netCDF-4/HDF5 variable, the HDF5 library opens a cache for that variable.

The default size of that cache (settable with the –with-chunk-cache-size at netCDF build time).

For good performance your chunk cache must be larger than one chunk of your data - preferably that it be large enough to hold multiple chunks of data.

In addition, when a file is opened (or a variable created in an open file), the netCDF-4 library checks to make sure the default chunk cache size will work for that variable. The cache will be large enough to hold N chunks, up to a maximum size of M bytes. (Both N and M are settable at configure time with the –with-default-chunks-in-cache and the –with-max-default-cache-size options to the configure script. Currently they are set to 10 and 64 MB.)

To change the default chunk cache size, use the set_chunk_cache function before opening the file with nc_set_chunk_cache(). Fortran 77 programmers see NF_SET_CHUNK_CACHE). Fortran 90 programmers use the optional cache_size, cache_nelems, and cache_preemption parameters to nf90_open/nf90_create to change the chunk size before opening the file.

To change the per-variable cache size, use the set_var_chunk_cache function at any time on an open file. C programmers see nc_set_var_chunk_cache(), Fortran 77 programmers see NF_SET_VAR_CHUNK_CACHE, ).


Generated on Tue Jul 9 2013 19:18:12 for netCDF. NetCDF is a Unidata library.