The limit for length of MPI identifiers was removed. Prior to MPI-4.0, MPI identifiers were limited to 30 characters (31 with the profiling interface). This limitation was initially introduced to avoid exceeding the limit on some compilation systems.
Rationale.
For Fortran, this limit was already relaxed for the Fortran specific function names,
see Section Interface Specifications, Procedure Names, and the Profiling Interface, and the Fortran language specification 2003
requires support for a minimum of 63 characters for internal and external identifiers.
Starting with the ISO/IEC 9899:1999 C programming language standard,
support for a minimum of 63 characters is required for internal identifiers,
but only 31 characters are required to be significant for external identifiers.
At the time of the release of MPI-4.0, most or nearly all compilers allow external
identifiers longer than 31 characters. Therefore, the restriction is removed.
( End of rationale.)
Advice to users.
This affects users only if they store MPI identifiers into fixed sized strings.
( End of advice to users.)