11.11. Building heterogeneous MPI applications
Heterogeneous support (specifically: supporting different sized and/or represented data types in a single MPI application run) within a single MPI job is technically required by the MPI standard.
However, there are both theoretical and practical problems with supporting true data heterogeneity at run-time.
Indeed, it is quite uncommon for production HPC environments to be data-heterogeneous (e.g., natively support little-endian on some nodes and big-endian on other nodes in the same MPI application job).
As such, supporting data heterogeneity is a feature that has fallen into disrepair and is currently known to be broken in this release of Open MPI.