[mpich-discuss] The max amount of data each process can send in MPI_Alltoallv

Huiwei Lu huiweilu at mcs.anl.gov
Fri Dec 13 17:18:42 CST 2013

Hi, folks,

What’s the max amount of data each process can send in MPI_Alltoallv? http://www.mcs.anl.gov/research/projects/mpi/www/www3/MPI_Alltoallv.html

As I understand, the input parameter of sendcnts is an array of int, so the amount of data each process can send is limited to MAX_INT (approximately 2G).

What if I want to use MPI_Alltoallv-like MPI routines to send a buffer of data that exceeds 2GB? Does it need to cut the data buffers to smaller sizes? Is there an easy way to do this? The reason I am asking is one of my distributed sort algorithm uses MPI_Alltoallv to distribute data after partitioning; it crashed when I tried to send in each process more than 2GB data.

Huiwei Lu
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