[mpich-discuss] MPI I/O using large integers in file type

[Nick Stokes]

Dear Rajeev,

On Wed, Sep 7, 2011 at 3:27 PM, Nick Stokes
<randomaccessiterator at gmail.com>wrote:

>
>
> On Wed, Sep 7, 2011 at 3:22 PM, Rajeev Thakur <thakur at mcs.anl.gov> wrote:
>
>> MPI_Type_create_hindexed does.
>>
>>
>
Moreover, on my 32-bit system  MPI_Aint is typedef'ed to int (at least in my
installation of MPICH2 - 1.3.3 on Windows 32-bit).  So hindexed type
seems not to solve the large file problem in general.  If it were possible
to create an indexed type with MPI_Offset displacements, that would have
helped.

Maybe I am on the wrong track here. Does my question make sense?  Perhaps a
more explicit and perhaps more relate-able example would be as follows:

Imagine a simulation where there are a total of 10^9  degrees of freedom,
and double precision is used.  The computation result is to be output to a
single file, which would add up to 8 GBs.  MPI is utilized to implement
parallelization via domain partitioning, and each partition holds a certain
chunk of data.   These chunks correspond to non-overlapping regions with
gaps in the final output.   How would you do a collective READ/WRITE in such
a case without integer overflow?

thanks many
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