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Diffstat (limited to 'release_docs')
| -rw-r--r-- | release_docs/RELEASE.txt | 25 |
1 files changed, 25 insertions, 0 deletions
diff --git a/release_docs/RELEASE.txt b/release_docs/RELEASE.txt index db946a0..db3e4e0 100644 --- a/release_docs/RELEASE.txt +++ b/release_docs/RELEASE.txt @@ -62,6 +62,31 @@ New Features Parallel Library: ----------------- + - Optimize parallel open/location of the HDF5 super-block + + Previous releases of PHDF5 required all parallel ranks to + search for the HDF5 superblock signature when opening the + file. As this is accomplished more or less as a synchronous + operation, a large number of processes can experience a + slowdown in the file open 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 |