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Subject: Re: [OMPI users] Can't read more than 2^31 bytes with MPI_File_read, regardless of type?
From: Richard Shaw (jrs65_at_[hidden])
Date: 2012-08-07 18:02:51


On Tuesday, 7 August, 2012 at 12:21 PM, Rob Latham wrote:
> Hi. Known problem in the ROMIO MPI-IO implementation (which OpenMPI
> uses). Been on my list of "things to fix" for a while.

Ok, thanks. I'm glad it's not just us.

Is there a timescale for this being fixed? Because if it's a long term thing, I would suggest it might be worth putting a FAQ entry on it or something similar? Especially as it's quite contradictory to most peoples interpretation of the specification. Maybe it's already listed as a known problem somewhere, and I just missed it - it took quite a while before I stopped thinking it was an issue with my code.

Is there a better workaround than just splitting the MPI_File_read up into multiple reads of <2^31 bytes? We're actually trying to read in a distributed array, and the workaround awkwardly requires the creation and reading of multiple darray types, each designed to read in the correct number of blocks less than 2^31 bytes. This seems like it could be a bit fragile.

Thanks again,
Richard