I don't know whether it's as bad as a deadly sin, but for us parallel writes are a huge problem and we get complete garbage in the file. Take a look at:
Implementing MPI-IO Atomic Mode and Shared File Pointers Using MPI One-Sided Communication, Robert Latham,Robert Ross, Rajeev Thakur, International Journal of High Performance Computing Applications, 21, 132 (2007).
They describe an implemenation of a "mutex" like object in MPI. If you protect writes to the file with an exclusive lock you can serialize the writes and make use of NFS's close to open cache coherence.
On Tue, Feb 2, 2010 at 08:27, Laurence Marks <Lfirstname.lastname@example.org> wrote:
I have a question concerning having many processors in a mpi job all
write to the same file -- not using mpi calls but with standard
fortran I/O. I know that this can lead to consistency issues, but it
can also lead to OS issues with some flavors of nfs.
At least in fortran, there is nothing "wrong" with doing this. My
question is whether this is "One of the Seven Deadly Sins" of mpi
programming, or just frowned on. (That is, it should be OK even if it
leads to nonsense files, and not lead to OS issues.) If it is a sin, I
would appreciate a link to where this is spelt out in some "official"
document or similar.
Department of Materials Science and Engineering
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email: L-marks at northwestern dot edu
Chair, Commission on Electron Crystallography of IUCR
Electron crystallography is the branch of science that uses electron
scattering and imaging to study the structure of matter.
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