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authorRichard Warren <Richard.Warren@hdfgroup.org>2017-10-10 13:47:22 (GMT)
committerRichard Warren <Richard.Warren@hdfgroup.org>2017-10-10 13:47:22 (GMT)
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Update the MANIFEST and release_docs/RELEASE files
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@@ -62,6 +62,31 @@ New Features
Parallel Library:
-----------------
+ - Optimize parallel open/location of the HDF5 super-block
+
+ Previous releases of PHDF5 allow all parallel ranks to
+ read the starting elements in a file to validate and process
+ the HDF5 super-block. As this is accomplished more or less as
+ a synchronous operation, a large number of processes will
+ likely experience a slowdown due to filesystem contention.
+
+ As a first step in improving the startup/file-open performance,
+ we allow MPI rank 0 of the associated MPI communicator to locate
+ the base offset of the super-block and then broadcast that result
+ to the remaining ranks in the parallel group. Note that this
+ approach is utilized ONLY during file opens which employ the MPIO
+ file driver in HDF5 by previously having called H5Pset_fapl_mpio().
+
+ HDF5 parallel file operations which do not employ multiple ranks
+ e.g. specifiying MPI_COMM_SELF (whose MPI_Comm_size == 1)
+ as opposed to MPI_COMM_WORLD, will not be affected by this
+ optimization. Conversely, parallel file operations on subgroups
+ of MPI_COMM_WORLD are allowed to be run in parallel with each
+ subgroup operating as an independant collection of processes.
+
+ (RAW – 2017/10/10, HDFFV-10294)
+
+
- Large MPI-IO transfers
Previous releases of PHDF5 would fail when attempting to