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| -rw-r--r-- | release_docs/RELEASE.txt | 24 |
1 files changed, 23 insertions, 1 deletions
diff --git a/release_docs/RELEASE.txt b/release_docs/RELEASE.txt index 20d58b3..4335b37 100644 --- a/release_docs/RELEASE.txt +++ b/release_docs/RELEASE.txt @@ -62,7 +62,29 @@ New Features Parallel Library: ----------------- - - + - Large MPI-IO transfers + + Previous releases of PHDF5 would fail when attempting to + read or write greater than 2GB of data in a single IO operation. + This issue stems principally from an MPI API whose definitions + utilize 32 bit integers to describe the number of data elements + and datatype that MPI should use to effect a data transfer. + Historically, HDF5 has invoked MPI-IO with the number of + elements in a contiguous buffer represented as the length + of that buffer in bytes. + + Resolving the issue and thus enabling larger MPI-IO transfers + is accomplished first, by detecting when a user IO request would + exceed the 2GB limit as described above. Once a transfer request + is identified as requiring special handling, PHDF5 now creates a + derived datatype consisting of a vector of fixed sized blocks + which is in turn wrapped within a single MPI_Type_struct to + contain the vector and any remaining data. The newly created + datatype is then used in place of MPI_BYTE and can be used to + fulfill the original user request without encountering API + errors. + + (RAW – 2017/07/11, HDFFV-8839) Fortran Library: ---------------- |