2.20 Set HDF5 Chunk Cache for Future File Opens/Creates: nc_set_chunk_cache
This function changes the default chunk cache settings in the HDF5
library for all variables in the file. The settings apply for
subsequent file opens/creates. This function does not change the chunk
cache settings of already open files.
For more information, see the documentation for the H5Pset_cache()
function in the HDF5 library at the HDF5 website:
http://hdfgroup.org/HDF5/.
Usage
int nc_set_chunk_cache(size_t size, size_t nelems, float preemption);
size- The total size of the raw data chunk cache, in bytes. This should be
big enough to hold multiple chunks of data.
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 1 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 one means fully read chunks are always preempted before other
chunks.
Return Codes
NC_NOERR- No error.
NC_EINVAL- Preemption must be between zero and one (inclusive).
Example
This example is from libsrc4/tst_files.c:
#include <netcdf.h>
...
#define NEW_CACHE_SIZE 32000000
#define NEW_CACHE_NELEMS 2000
#define NEW_CACHE_PREEMPTION .75
/* Change chunk cache. */
if (nc_set_chunk_cache(NEW_CACHE_SIZE, NEW_CACHE_NELEMS,
NEW_CACHE_PREEMPTION)) ERR;
/* Create a file with two dims, two vars, and two atts. */
if (nc_create(FILE_NAME, cflags|NC_CLOBBER, &ncid)) ERR;
...
