6.6 Set HDF5 Chunk Cache for a Variable: NF_SET_VAR_CHUNK_CACHE
This function changes the chunk cache settings for a variable. The
change in cache size happens immediately. This is a property of the
open file - it does not persist the next time you open the file.
For more information, see the documentation for the H5Pset_cache()
function in the HDF5 library at the HDF5 website:
http://hdfgroup.org/HDF5/.
Usage
nc_set_var_chunk_cache(int ncid, int varid, size_t size, size_t nelems,
float preemption);
ncid- NetCDF ID, from a previous call to nc_open or nc_create.
varid- Variable ID.
size- The total size of the raw data chunk cache, in megabytes. This should be
big enough to hold multiple chunks of data. (Note that the C API uses
bytes, but the Fortran APIs uses megabytes to avoid numbers that can't
fit in 4-byte integers.)
nelems- The number of chunk slots in the raw data chunk cache hash table. This
should be a prime number larger than the number of chunks that will be
in the cache.
preemption- The preemtion value must be between 0 and 100 inclusive and indicates
how much chunks that have been fully read are favored for
preemption. A value of zero means fully read chunks are treated no
differently than other chunks (the preemption is strictly LRU) while a
value of 100 means fully read chunks are always preempted before other
chunks. (The C API uses a float between 0 and 1 for this value).
Return Codes
NF_NOERR- No error.
NF_EINVAL- Preemption must be between zero and 100 (inclusive).
Example
This example is from nf_test/ftst_vars2.F:
include 'netcdf.inc'
...
C These will be used to set the per-variable chunk cache.
integer CACHE_SIZE, CACHE_NELEMS, CACHE_PREEMPTION
parameter (CACHE_SIZE = 8, CACHE_NELEMS = 571)
parameter (CACHE_PREEMPTION = 42)
...
C Set variable caches.
retval = nf_set_var_chunk_cache(ncid, varid(i), CACHE_SIZE,
& CACHE_NELEMS, CACHE_PREEMPTION)
if (retval .ne. nf_noerr) call handle_err(retval)
