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

Rajeev Thakur thakur at mcs.anl.gov
Fri Dec 13 19:02:47 CST 2013

You can create a contiguous datatype of size 1GB and then send 1G items of that size :-).

On Dec 13, 2013, at 5:18 PM, Huiwei Lu <huiweilu at mcs.anl.gov> wrote:

> 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.
> Thanks.
> --
> Huiwei Lu
> http://www.mcs.anl.gov/~huiweilu/
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