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-rw-r--r--release_docs/RELEASE.txt24
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:
----------------