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[svn-r5430] Purpose:

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Document Bug fix/Code improvement below:

Description:
    Currently, the chunk data allocation routine invoked to allocate space for
    the entire dataset is inefficient.  It writes out each chunk in the dataset,
    whether it is already allocated or not.  Additionally, this happens not
    only when it is created, but also anytime it is opened for writing, or the
    dataset is extended.  Worse, there's too much parallel I/O syncronization,
    which slows things down even more.

Solution:
    Only attempt to write out chunks that don't already exist.  Additionally,
    share the I/O writing between all the nodes, instead of writing everything
    with process 0.  Then, only block with MPI_Barrier if chunks were actually
    created.
This commit is contained in:
Quincey Koziol 2002-05-17 07:54:42 -05:00
parent a6b4cba798
commit e02ae065f6
1 changed files with 8 additions and 4 deletions
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12
release_docs/RELEASE.txt
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@ -164,6 +164,10 @@ Documentation
New Features
============
* Changed method for allocating chunked dataset blocks in parallel to only
allocate blocks that don't already exist, instead of attempting to create
all the blocks all the time. This improves parallel I/O performance for
chunked datasets. QAK - 2002/05/17
* Allowed the call to MPI_File_sync to be avoided when the file is going to
immediately be closed, improving performance. QAK - 2002/05/13
* Allow the metadata writes to be shared among all processes, easing the
@ -184,9 +188,12 @@ New Features
datatype conversion is unneccessary. QAK - 2002/04/02
* Improved performance of single hyperslab I/O when datatype conversion is
unneccessary. QAK - 2002/04/02
* New API function H5Dset_extent. Modifies the dimensions of a dataset,
allows change to a lower dimension. The unused space in the file is freed.
PVN - 2002/03/31
* Added new "H5Sget_select_type" API function to determine which type of
selection is defined for a dataspace ("all", "none", "hyperslab" or
"point"). QAK - 2002/02/7
"point"). QAK - 2002/02/07
* Added support to read/write portions of chunks directly, if they are
uncompressed and too large to cache. This should speed up I/O on chunked
datasets for a few more cases. QAK - 2002/01/31
@ -279,9 +286,6 @@ New Features
* A helper script called ``h5cc'', which helps compilation of HDF5
programs, is now distributed with HDF5. See the reference manual
for information on how to use this feature.
* New API function H5Dset_extent. Modifies the dimensions of a dataset,
allows change to a lower dimension. The unused space in the file is freed.
PVN - 2002/03/31
Support for new platforms and languages
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