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SDsetchunkcache
intn SDsetchunkcache(int32
sds_id
, int32
maxcache
, int32
flags
)
sds_id
IN:
SD interface identifier returned from
SDstart
maxcache
IN:
Maximum number of chunks in the cache
flags
IN:
Flags determining the behavior of the routine
Purpose
Determines the size of the chunk cache.
Return value
Returns SUCCEED (or 0) if successful and FAIL (or -1) otherwise.
Description
By default, when a generic SDS is promoted to be a chunked SDS, the maxcache parameter is set to the number of chunks along the last dimension and a cache for the chunks is created.
If the chunk cache is full and the value of the maxcache parameter is larger than the currently allowed maximum number of cached chunks, then the maximum number of cached chunks is reset to the value of maxcache. If the chunk cache is not full, then the size of the chunk cache is reset to the value of maxcache only if it is greater than current number of chunks in the cache.
Never set the value of maxcache to be less than the number of chunks along the last dimension of the biggest slab to be written or read via
SDreaddata
or
SDwritedata
. Doing this will cause internal thrashing. See the section on chunking in Chapter 13 of the HDF User's Guide, titled
HDF Performance Issues
, for more information on this.
Currently the only allowed value of the flags parameter is 0, which designates default operation. In the near future, the value HDF_CACHEALL will be supported to be used to specifiy that the whole SDS object is to be cached.
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HDF User's Reference Manual, Draft 06/09/97, NCSA HDF Development Group.