Maximum amount of data that can be sent using MPI::Send

Question

With the syntax for MPI::Isend as

MPI::Request MPI::Comm::Isend(const void *buf, int count, 
              const MPI::Datatype& datatype, 
                       


        

Answer 1

I haven't done MPI, however, int is the usual limiting size of an array, and I would suspect that is where the limitation comes from.

In practice, this is a fairly high limit. Do you have a need to send more than 4 GB of data? (In a single Isend)

For more information, please see Is there a max array length limit in C++?

Do note that link makes references to size_t, rather than int (Which, for all intents, allows almost unlimited data, at least, in 2012) - however, in the past, 'int' was the usual type for such counts, and while size_t should be used, in practice, a lot of code is still using 'int'.