Unify handling of collective metadata reads status (#1206)

1 files changed, 21 insertions, 0 deletions

diff --git a/release_docs/RELEASE.txt b/release_docs/RELEASE.txt
index bba27c9..ece00cc 100644
--- a/release_docs/RELEASE.txt
+++ b/release_docs/RELEASE.txt
@@ -1083,6 +1083,27 @@ Bug Fixes since HDF5-1.12.0 release
 
       (DER - 2021/11/23, HDFFV-11286)
 
+    - Unified handling of collective metadata reads to correctly fix old bugs
+
+      Due to MPI-related issues occurring in HDF5 from mismanagement of the
+      status of collective metadata reads, they were forced to be disabled
+      during chunked dataset raw data I/O in the HDF5 1.10.5 release. This
+      wouldn't generally have affected application performance because HDF5
+      already disables collective metadata reads during chunk lookup, since
+      it is generally unlikely that the same chunks will be read by all MPI
+      ranks in the I/O operation. However, this was only a partial solution
+      that wasn't granular enough.
+
+      This change now unifies the handling of the file-global flag and the
+      API context-level flag for collective metadata reads in order to
+      simplify querying of the true status of collective metadata reads. Thus,
+      collective metadata reads are once again enabled for chunked dataset
+      raw data I/O, but manually controlled at places where some processing
+      occurs on MPI rank 0 only and would cause issues when collective
+      metadata reads are enabled.
+
+      (JTH - 2021/11/16, HDFFV-10501/HDFFV-10562)
+
     - Fixed several potential MPI deadlocks in library failure conditions
 
       In the parallel library, there were several places where MPI rank 0