This section describes the manipulation of communicators in MPI. Operations that access communicators are local and their execution does not require interprocess communication. Operations that create communicators are collective and may require interprocess communication.
Advice to implementors.
High-quality implementations should
amortize the overheads associated with the creation
of communicators (for the same group, or subsets thereof)
over several calls, by allocating multiple contexts with one
( End of advice to implementors.)