+1 on Nick's responses. AFAIK, if you don't mind getting garbage in the output file, it should be fine to do. Specifically: it should not cause OS issues (crash, reboot, corrupted filesystem, etc.) to do this -- but the file contents will likely be garbage.
That being said, this situation likely falls into the "Doc, it hurts when I do this..." category. Meaning: you know it's wrong, so you probably shouldn't be doing it anyway. :-) On Feb 2, 2010, at 4:50 PM, Nicolas Bock wrote: > Hi Laurence, > > 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. > > nick > > > On Tue, Feb 2, 2010 at 08:27, Laurence Marks <l-ma...@northwestern.edu> 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. > > -- > Laurence Marks > Department of Materials Science and Engineering > MSE Rm 2036 Cook Hall > 2220 N Campus Drive > Northwestern University > Evanston, IL 60208, USA > Tel: (847) 491-3996 Fax: (847) 491-7820 > email: L-marks at northwestern dot edu > Web: www.numis.northwestern.edu > Chair, Commission on Electron Crystallography of IUCR > www.numis.northwestern.edu/ > Electron crystallography is the branch of science that uses electron > scattering and imaging to study the structure of matter. > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users > > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users -- Jeff Squyres jsquy...@cisco.com
