Hi Larry,
Thank you very much for the explanation, because it wasnt clear in the
documentation.
--
Fernando Puech Helguero
De: Hdf-forum [mailto:[email protected]] En nombre de
Larry Knox
Enviado el: martes, 04 de noviembre de 2014 16:33
Para: [email protected]
Asunto: Re: [Hdf-forum] Question about chunk cache
_____
From: Hdf-forum <[email protected]> on behalf of Fernando
Puech Helguero <[email protected]>
Sent: Friday, October 31, 2014 12:13 PM
To: [email protected]
Subject: [Hdf-forum] Question about chunk cache
Ive created a chunked dataset and created a chunk cache when writing to the
file. After closing the h5 file and reopening it. Do I have to recall
H5Pset_chunk_cache to set the appropriate chunk cache or when I call H5Dopen
the cache is automatically created for reading?
Best regards
--
Fernando Puech Helguero
Hi Fernando,
The chunk cache size is a property of accessing a dataset and is not stored
with the dataset or the file. If you want to guarantee the same chunk cache
settings each time H5Dopen is called, you will need to call H5Dopen with a
dataset access property list (H5Dopen( hid_t loc_id, const char *name, hid_t
dapl_id )) where the chunk cache size is set by calling H5Pset_chunk_cache
for that property list. The property list can be used for multiple accesses
in the same application.
For files where the same chunk cache size will be appropriate for all or
most datasets, H5Pset_cache can be called with a file access property list
to set the chunk cache size for accessing all datasets in the file.
Both methods can be used in combination, in which case the chunk cache size
set by H5Pset_cache will apply except for specific datasets where H5Dopen is
called with dataset property list with the chunk cache size set by
H5Pset_chunk_cache.
In the absence of any cache settings, H5Dopen will by default create a 1 MB
chunk cache for the opened dataset. If this size happens to be appropriate
you dont have to call either function to set the chunk cache size.
It is also possible that a change in access pattern for later access to a
dataset will change the appropriate chunk cache size. For more detailed
information on chunks, chunk caching, and performance pitfalls please see
Chunking in HDF5 at
htttp://www.hdfgroup.org/HDF5/doc/Advanced/Chunking/index.html.
Larry Knox
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